We'll start with the basic hand tools:
1. Set of phillips screwdrivers from tiny to large.
2. Set of plain screwdrivers from tiny to large.
3. Set of robertson screwdrivers from tiny to large.
4. Set of torx drivers.
5. Good set of hex keys.
6. Vise grips (needle nose and regular)
7. Pliers (needle nose, bent needle, regular)
8. 6-8" crescent wrench.
9. 3 hammers (light 6 or 8 oz) one plastic, one heavy deadblow.
10. Set of files including a grobert or swiss #2 or #4 for impressioning.
11. Cleaning card, or brush to clean files.
12. Set of chisels 3/4", 1" 1 1/4".
13. 8" Level
14. Pencil, marker
15. Auto center punch, pin punch, center punch, awl
16. Set of Tin snips (right, left, center)
17. Multi-driver screwdriver w/various bits and including security bits.
18. Flashlight.
19. One of them disposable carpenter's knives where you can replace the blades.
20. Imperial/Metric tape measure.
21. Calculator
22. Machinist square 12" & carpenter's square
23. Digital Caliper.
24. Set of picks (regular, tubular, pickgun), key extractors, depth keys, turning wrenches for lock roses, unican combo lock change keys.
25. Can of spray lubricant, lock de-icer
26. Wire cutters/strippers/crimpers.
27. Pipe wrench, crowbar, brass drift.
28. Snap-ring pliers (reversible)
29. Formed end long tweezers.
30. Set of plug followers and cap removal tools.
31. Electrical tape.
32. Duct tape.
33. Roll of wire.
34. Hand plane for fitting doors etc.
35. Roll of shop towels and hand cleaner.
36. Hacksaw and spare blades.
37. 9" Borescope (not mandatory unless you're doing safe work)
38. 3/8" & 1/2" Socket and ratchet set
39. Set of Nut drivers.
40. Set of wrenches/spanners 3/8-15/16 and metric 3-15mm
41. Complete set of auto opening tools + manuals/updates.
42. 2' & 5' Step-ladder.
43. Dustpan and brush.
44. Garbage bags or box for debris such as broken lock parts, etc.
45. Tap & die set.
46. Portable work table/surface and stool.
47. Extending Magnet.
48. Jig/knockout for cam lock installation.
49. Digital Camera.
50. Compression plate and steering wheel removal tools.
Some type of carrying cases for all of the above.
Alrighty..next on the list, my personal favorite...POWER TOOLS!
1. 18V 1/2" Cordless drill with extra batteries, charger, and hole saws. 1/2",3/4",1",1 1/4", 1 1/2", 2 1/8". Set of titanium/cobalt bits 1/16 to 3/4". Masonry bits 1/4", 3/8", 1/2", 3/4", assortment of uni-bits.
2. 9.6V 3/8" Cordless drill or screwdriver, extra batteries, charger, and bits.
3. 1/2" Hammer Drill (Corded), Lever Rig, Safe Bits.
4. Good key duplicating machine such as the Silica Bravo Semi-auto.
5. Good code machine such as the 1200 Blitz or ITL-950 or 950C +software of course.
6. Scotsman Tubular key machine.
7. Laptop computer, printer, and cell phone.
8. 2-3000 watt power inverter
9. Dremel tool with accesories such as cut-off wheels, router attachment, etc.
10. High speed router.
11. Jigsaw. (if you install/repair wood door frames.)
12. Mortising Jig.
13. Couple of extension cords. Thanks to I Pik U for that addition.
14. 4" & 6" angle grinder
Pin kits:
This will depend on what area of the world you are located in, but for now I'm going to assume you're in the America's. Hopefully a U.K. lockie will come on and give some suggestions for some of the particular lever tumbler locks found there. In the meantime, here are my suggestions:
1. Lab .003 or .005 Wedge or Super Wedge. If you plan on performing masterkey systems, especially for larger stores/buildings/malls/hospitals, etc...you will really find the .003 pin kit more to your liking. The Super Wedge differs only from the standard in that it contains a bottom drawer for small tools, extra pins, keyblanks, parts, etc... This one pin kit will allow you to cover most pin tumber locks such as Arrow, Corbin, Kwikset, Sargent, Schlage, Segal, Taylor, Weiser, Weslock, Yale, and many more, so one of these is a must-have item.
2. Cam lock wafer kit. This simple kit will allow you to rekey most rekeyable wafer locks. This is really a must have item and will save you stocking dozens of different types of cam locks.
3. Tubular pin kit. If you plan on servicing these locks, this'll be a good thing to have. Most of these brand specific kits also include some of the most common parts such as springs, clips, screws, and other replacement parts. (I personally don't see many, so it's generally easier for me to just replace, or decode and order keys). Not necessary as a starter item, but something to consider as your business grows.
4. Automotive. This is a biggie, really, and the only way to know (if you plan on doing automotive) what you're going to see is to tour your city/town, and write down a list of the most common types of auto's (don't forget motorcycles) that you see. Your best bet would to then contact your supplier for some catalogs, and start shopping. You'll find that certain kits will cover more than one type of locking system, and these are the ones you want. For example, Strattec has many kits for Ford. They have particular ones for the old 5-pin system, the 8-wafer, and 10 wafer system...they also have more general (and of course, more expensive) kits that will cover all of these. You will need to determine from your own city/town what is the most popular. An easy way is to find out what dealerships are in your town/area that you'll be covering, and purchase equipment for those. The three big ones GM, Ford, and Chrysler kits should be enough to get you started if you choose to service automotive. Hint: Be cautious when purchasing these kits as they can be expensive, and if you aren't going to use them often it's kind of a waste of money.
5. Padlock kits. Companies such as American and Master Lock have pin kits specifically for their brand of locks, as does Papaiz and several others. What American and Master Lock WON'T tell you is that their pin sizes (though "numbered" differently), will interchange.

6. Interchangeable core kits. Yeah, if you plan on servicing these locks, you will need brand specific kits to do so. This is NOT a recommended starter item unless you are sure you will get this type of work.
7. At some point and time you may decide you wish to have your own restricted and/or high security keyway. In your inital package you should receive a special pinning kit + tools in many cases, to be able to properly deal with those types of locks.
Inventory
Wow....I was going through the key book looking at what should be included, and decided for the sake of time and space to share with you some bits of opinion and experience instead of listing specific keys.
A. Vehicle keys:
The best way to determine what you will need as far as key inventory for automotive is very simple. A couple of hours a day, at various times, take with you a pen and pad and go to a coffee shop or popular cafe that has a window seat with a good view of your main roads. Spend a couple hours making notes on the make/model/ and approximate year of vehicles that you see drive by. This does a couple things for you.
1. Helps you to learn to identify the vehicle as you arrive on-site and speeds your selection of tools.
2. Gets you into the habit of mentally choosing a keyblank and/or opening tool.
3. Will enable you to quicikly determine if a particular vehicle is transponder equipped. (Whether this is good or bad depends on the type of business you are after.)
Also, take a drive through used car lots and talk the sales people (drop off cards too) to see what the "fast movers" are. After about a week or so you should have a pretty good idea of what the popular vehicles are in town. Don't forget to include motorcylces, RV's and large semi-trailer trucks (if you have 'em) on your list as well. Through your supplier you should be able to receive (for free) Strattec and Ilco parts books, key identification books, programming instructions, and automotive tool lists so that you can decide what types of keys you will need. Be sure to look through the books carefully, as there are more than a few keyblanks that will work on a range of vehicles. Talk to a local locksmith or two about what keyblanks will interchange with what. This will save greatly on your inventory costs.
For the America's your main automotive keys will be from the big three. GM (P1098A and S1098B are examples), Ford (1196FD and S1196 will work in a large variety of Fords), and Chrysler (Y157 and Y155 are popular). Euro vehicles are famous for having keyblanks that will interchange between a variety of manufactures and locks (X121 is a good example of that). Looking through a keyblank book, you can compare the profiles to cut down on the types of blanks required.
B. Residential
Again, a simple tour through your town should yield good results. I would advise taking mental notes, though, since residents might find it suspicious seeing you stand in front of their door with a paper and pen in hand. Another good way of identifying popular types is simply to ask your friends and neighbors to have a look at their keyrings and take notes from there.
C. Commercial
Make it a habit that every business you walk into that you glance at their locks and hardware. Some will have the brand name stamped right on the face which makes it easy to identify. Padlocks, and other security devices like that will most likely have a name stamped right on them, and will be easy to identify.
D. Miscellaneous keys
These would include filing cabinet, safe deposit, drawer locks, etc. This is a tricky call since there are literally hundreds of different types, and many do not have identify marks of any kind. Purchasing a variety of different keyblanks, and good conversation with a supplier and other locksmiths will help you to identify what you will need to carry.
A word of warning: Do not soley trust your supplier(s). Although they will be helpful, some will occasionally try to take the opportunity to offload some "oddball" blanks on an unsuspecting client.
Thanks to HeadhunterCEO for bringing up the issue of necessary parts...I've added his recommendations, and started a new section in this post for parts and other "extra necessities".
Parts
Fasteners:
Pan & flat , Short and long. Self tappers would be the best
6-32
8-32
10-24
10-32
12-24
1/4-20
5/16-18
-Lag,hex,nuts and carriage bolts Short and Long
1/4-20
5/16-18
3/8-16
1/2-13
Some wood screws but definately these short and long
#6 brass and 26d
screws for butt hinges
-Washers for all your lags
-Sleeve anchors for use with the lags to bolt things down
-plastic anchors for blown out screw hole repairs and anchoring thresholds
-sex bolts,sex bolts,sex bolts!
-springs, and c-clips of various dimensions.
Random:
Bondo- cream &xtra tube of hardener
J&B weld
caulk gun
caulk duronotic,clear,black,brown
Lubriplate grease
cutting/tapping fluid or
drill lube fluid/wax (i like wax)
metal stock for those "quickie" repairs in various lengths and thickness.
Alum L bar 1"x1 1/2
1/8 mild steel plates of various sizes
More will be added as I have time. I'll leave this unlocked, and if there's something you think I missed for a particular section, feel free to post.