Store your food supply at least 3 to 6 inches off the ground, and away from walls.
This helps ensure that your food supply remains safe from rodents, insects, and moisture.
Bugs and insects like to crawl along the edges of the floor and walls (and across the floors), so if the bottom layer of your stack begins several inches (mostly) out of reach from a wall or floor, then this will greatly reduce the odds of external sources of insect contamination.
It will also eliminate the problems associated with storing food containers directly on the concrete floors, which include moisture from the concrete seeping in to corrode metal and dampen paper sacks or other absorbing materials.
To avoid all of these problems, you might consider using wooden pallets.
You can often pick up used wooden pallets from businesses which take delivery of their inventory that way. This will save them from dealing with disposal. Use common sense and avoid very dirty or badly weather damaged pallets or those which may themselves be carrying insects. Regardless though – clean them well when you get home.
You could also simply build your own pallet structure to hold your stacks of emergency food off the floor. 2×4′s and cheap pine boards (and some nails or screws) will work just fine…