the first tention wrench I used, was a small flat end scredriver. After considerable time, effort, and sore fingers, I managed to use a hammer to bend the tip so it was at around 20 degree. This ment I could use it with out the handle getting in the way of my picking hand.
The metal straps sometimes used to secure and seal palets of cargo are also great, as you can cut the ends to use it as a two point to tention wrench for say wafter locks etc. Personally thou, I would highly advise you to get in touch with someone who can get you a decent first set. Learning to improvise will always prove a life long useful skill, but it will hinder your development and might never get you picking some of the more decent stuff out there.