5 gallon buckets with a lid make an excellent camping tool.
A.) They make for a waterproof container. Oddly shaped, but usually decent for stuffing a sleeping bag and tarp. For car camping they work fine. Boat camping can be a little iffy. It's not terribly hard to strap one to a kayak on the outside. Backpacking? You can pretty much forget about it.
B.) They are an excellent camping seat/chair. Reasonable height for most people, and the lid makes it stable enough to sit on.
C.) Water Bucket: should you need to clean or carry water more in bulk than by the bottle.
In total, you've got a 3 use minimum tool. Obviously buckets are not as easy to carry as a bag, but in a boat, that doesn't matter as much.