Good old curious george style boats are generally the best. They displace a decent amount of water, are very stable, and the center can have a little flag taped to it. I know without pictures instructions can be confusing, but considering they are so easy, I think you can handle it.
Fold a sheet in half short ways. Fold it in half the other way, but unfold it this time, leaving a centerline crease. Fold the corners of the folded side to the centerline, making a point out of what was the folded side (like you were making a paper airplane). If you used 8-1/2 by 11 then you have a little bit of the non-folded side that you can fold down over each side. You should have a triangle that you can open into a peter pan hat. This will hold water and is a great way to make a cup if you desperately need one. You could also use this as your boat if you stick some weight in the bottom and use something to hold it open. Chances are it will just fall over and sink though...
Now all you have to do is half turn this inside out. Fold the point down to the middle of the open side to make a crease and unfold. This crease is just to make the next step easier. Open the hat and push the point in. You now have something that resembles a stupid sombrero or a curious george boat, depending on if it is on your head or in the water.
I made a flotilla of these in the waiting are at the pearl harbor thing and put them in the fountain there with bits of bread in them. Much to my amusement, the pigeons that swarm around there attacked and sank the boats. It was quite the reenactment.