I came off the water of my first Grand Canyon trip a couple weeks ago and couldn't have had a better time. The place was, of course, mind-blowingly incredible, and the people I was with were wonderful. The gear I brought: rainboots.
Packing for the Grand Canyon
Before I left for Arizona, I asked a guide friend of mine if she had any recommendations as to what things to bring that might not jump easily to mind. She said that she loved having rainboots for camp. I thought, "why not?" and brought my pair of $20 heavy duty rain boots along. None of the other 15 people on the trip had thought of the idea and I think some of them were a tinge jealous of this piece of functional footwear.
My feet were in better shape with the rainboots, and were kept toasty warm on chilly nights and mornings. Come evening every day, I would wash my feet, slap some salve all over them, pull on some wool socks and put them in the boots. My feet stayed warm and dry and relatively clean. In the mornings, if it was especially cold, I'd slip the boots back on and easily maneuver from shore to the boats to cook up a mean breakfast. For packing, I put them in two 2-gallon ziplocks and threw them in my drybag.
Rainboots are only for camp
While I could have used them on the boats a couple of times for colder, wetter days, I chose to only use them in camp. Rainboots are a definite hazard if you take a swim. They can fill up with water, creating a suction around your foot, leaving you unable to take them off and more susceptible to drowning. I would also only use them for longer trips, probably leaving them at home for anything shorter than a week. On a 21-day trip with six 18' boats, space was not a huge issue.
When you have extra space for a few superfluous comforts, I recommend rainboots on the river!