Windup lanterns can be okay, but most seem to relatively low quality. The first one I had, the crank handle broke off on one of the first outings it was brought along for. Somehow I ended up with another one and it is still working. That said, it doesn't really see heavy use; when outdoors I use a propane lantern so the battery one is used more for getting ready for bed inside the tent on family trips.

If I wanted to get a crank powered lantern, or anything really, that I intended to depend on I'd seriously consider something from Freeplay.

On the slingshot front, I don't have one, but I've heard really good things about A+ Slingshots. They seem like a great way to go.