re: In St Bernard they're giving every resident 10 sandbags...

I put a few in front of doors with the idea of helping to prevent water from coming under doors from passing vehicles / spray action.

I've also heard of people using them to elevate things.

Build a fort on the roof. Makes a good sniper nest to fire from at the looters

Other posters are right. It just keeps some waves from getting water into your front door. But I passed by this afternoon and there was no way I was waiting in the line of vehicles to get them. It was insane.