Large ziplock bags would fit, depending on what you put in them. I always save the zipper bags that blankets or quilts come in to use that way.

Try Bed Bath and Beyond. They sell a variety of risers. All the beds in my house now have risers and we have found large flat storage boxes , also from BBB. Great for collectibles, books, out of season clothes.

Our bed is also quite low to the ground. It's hard to describe, but the side rails are quite deep. I don't want to use risers because the top of the mattress is already high enough. I've more or less reconciled myself to not being able to put things under the bed. I do have two plastic boot trays that slide under my side of the bed. I can put flat shoes on them. That gets the shoes out of the way, but also fills some space so that things don't creep under the bed where they're very hard to retrieve.

jsginbuffalo, that's pretty ingenious!

You're killing 2 or 3 birds w/ one stone. Flat shoes have a place; under bed area is contributing; stuff can't get lost underneath there so easily.