>>504711A tarp like the one pictured is great. If you're feeling fancy: rig up sone mosquito netting sheets along the edge with some heavy duty clothes pins, just maje sure theyre pushed all thre way in so the tarp has sort of a lip over it and that you weigh the bottom down.
No need to shell out cash and use up carry space, for a tent. It's really all about preference, though. Buy a hammock, regardless; they're a good gift if you wind up hating them for scouting.