1: Where do you find scuba tanks with everything destroyed?
2: Where do you find gas or freeze orange juice with everything destroyed?
3: How do you pressurize it enough?

The idea behind the whole setting is that weapons like a flamethrower are INCREDBILY rare and valuable. :P Weapons like machetes or axes would be more common. Possibly a rotating saw blade if you can find batteries and a motor and rig it up. (solar panels can always give electricity after all)