Take along a boxful of the new adult diapers for outdoorsmen and women. Only have to change them twice a day. Instead of Pampers they are called Campers.
Aren't humans vain. As they walk behind their dogs, with a baggy over their hand, anticipating the pick up. Give your buddy a roll of baggies.
A pail is good. If your friend needs privacy when making a deposit get a jumbo sized black garbage bag he can pull over himself and sit under.