Yeah, I suspect that the OP's situation would change from 1-2 people in each house in his current situation, to everyone consolidating in a SHTF situation. I know that's what I would do. Get all the neighbors and supplies into one main location, so you can set up guard shifts, consolidate supplies, etc.
The sand in trash cans is a pretty good idea. It's also something you could put together very quickly, even after SHTF. Even using just your existing trash cans, and the dirt from your backyard... Ideally you might have some extra cans on hand, for just that purpose.