A drift chute, also known as a drift sock or sea anchor is a parachute for a vessel that is deployed in the water. It works like a parachute in air in that it slows you down. I use one a lot more than I would an anchor. Whenever the wind is blowing it will decrease your drift speed up to 2/3rds. Very handy when you can't anchor or don't want to and much safer in many areas. They won't work without wind however. In current they are carried along just like you. I never leave without one in the hatch, just in case.
As to size we use small boat ones. Usually they're 17-18". These sizes work well and store easily.