Many folks actually gain weight on these trips. Plates and utensils are provided. Outfitters do not normally provide alcohol of any kind. Passengers may bring their own personal poison. The system isn't perfect, but it's effective, private, and does the job.
All waste is carried out of the canyon.
Some outfitters set up little tents for the privy, but I prefer a good view of the river and fresh air. Driving to work is more dangerous - if you figure the odds. Outfitters and their boatmen are cautious, careful folks. Moreover, they are strictly licensed and regulated by the National Park Service. These trips are about as safe as they can get, given the nature of river running.