I thought it would be fun to make a raft out of recycled milk jugs. It was pretty straightforward, just plywood and jugs. It contains 62 bottles, and I used two pieces of 8x10' plywood for the body, and chicken wire for the bottom. Sorry I only have a couple photos, I didn't think to make a step by step guide. Maybe I will someday.
Anyway, I think the whole thing cost about $30, which was just wood and screws. Works pretty well, if I do say so myself.