I would go with any good size stainless steel bottle (say 26-32 Oz ish) as for the knife I would go with a Swiss army knife with a wood saw (maybe a vic farmer) as from your scenario there seems little danger and help nearby if needed,(sounds some what like testing your gear in your backyard)though like Byrd Huntr I'm whery of only having a T-shirt, a proper shirt seems better.

There's an interesting mod on the sosak forum where someone cut off a Philips screwdriver and put a brass tube over the stub to hold a flint that I think would be usefull