Leave No Trace
Besides many great thrills while paddling, many enjoy the solitude and raw beauty rivers provide. Even local runs like the Potomac are quite spectacular. It really saddens me when I see people toss trash on the river side. Our club and others in the area have performed numerous river clean-ups in association with the various park authorities. It isn't a bad practice to take along an extra trash bag and tote out small pieces of trash you encounter and dispose in the nearest receptacle. I also highly recommend properly securing gear in your boat so you don't lose anything if you happen to swim. If you severely wrap a boat and are unable to retrieve it (very unlikely with air bags), please contact the local Fire Department so they don't waste scarce resources looking for a non-existent drowned boater.
Most kayak trips are day trips which simplifies bathroom logistics a great deal. On day trips, it is very important to be discreet. Just like any long road trip, try to go before the trip in a regular bathroom facility. If you take this precaution, you will only need to deal with liquid waste. There are pro's and con's to peeing on land versus underwater. If you choose land, hike a good distance away from the river side to avoid stinking up the area. Larger streams provide an excellent dilution factor as long as you are not to close to shore. Most western rafting trips request you pee in the water and downstream of camp or assembly.
Solid waste issues are more challenging. If you go the burial route, you will need a small shovel and dry toilet paper of course. Bury roughly 6" underground and stay at least 200' from any water source. Heavily used parks and streams often have more stringent requirements such as usage of portable potties and carrying your waste out. Here is a good article on this very subject: Human Waste Procedures.
When washing up, please use bio-degradable soap like Doctor Bronners or Camp Suds and do so well away from the stream side. There are a number of hand sanitizer products on the market these days that can also be used and packed out which are perfect for day trips.
River trips are supposed to be fun, not a race. Schedule frequent breaks so people can stay well hydrated, take nature breaks, and make minor adjustments. I like to take these breaks at interesting places like play spots, nice beaches, etc. On a long day trip, I strongly recommend a lunch break. Some will eat, others will play close by river features. Set a time limit for lunch and let everyone know otherwise you may take far longer to reassemble than your float plan budgeted for. After lunch, do a quick inspection to make certain no one left any trash behind.