That trailer might have a padlock. If that's the case then for the pleasure of fiction we can assume it can be shimmed. A person could improvise a shim and slip the lock with only a soda can and a pocket knife in a perfect world scenario. It isn't as glorious of an idea as picking but it is something you could phone a friend and fumble through.
The more plausible picking scenario would be if it was a disc tumbler lock, and a trailer with T-handles would use them. I have a small Swiss Army knife that has a small blade that I can pick nearly all of the disc tumbler locks I've tried. Rock it up and down while turning it slightly, no need for a tension wrench. A street sweeper bristle found in a parking lot might work as-is as well.
I understand what you are going for. If it is just a padlock he is trying to pick, and it isn't expected to be top of the line, if he has or can find a couple paper clips, or sturdy wire (like from a thin chain link fence) it wouldn't be especially far fetched that he'd be able to McGuiver it into an improvised pick and tension tool... the same trick could likely be used for some fairly flimsy door locks....
And I can totally use a soda can, since there are already recycling bins in the parking lot.