One of my favorite things to fold up quick...it is very easy but has a trick ending, so to speak. Still, it comes in quite handy. I like to return change, keep pens or glasses in such boats. And they do float. Well, maybe not if you make it out of mesh or absorbent towels, but for the most part...
Here's a video on folding a utilitarian paper boat:
And included for the price, the written instructions: