In reply to captain paranoia:
> Even a domestic machine ought to be able to get through the fabric of a rucksack. If the waterproof coating is a problem, try rubbing some beeswax on the needle to help it slip through the PU coating.
I'd agree with this. I can sew through three layers of stiff nylon webbing with our cheap Singer machine without problems.
Although, I'd take the 'give them a strong needle and a thimble and say get on with it scouts!' approach.