Well, to offer a more serious answer, short term I'm a "bag it" fan. It's easy, allows you the convenience of still being able to sit on your throne, and doesn't require either water or physical labor. Organizing neighborhood collection points, using sacrificial C&C trash cans, would be a step towards keeping the community sanitary and free of contamination and disease. We should be able to manage that system for weeks if not months.
If we're talking longer term, like the world actually ended, I think composting is really the only viable option in my area.