Such great ideas. Everyone on here is so smart!

I have used flexible kitchen cutting mats that come in packages of three, each about the size of a cookie sheet.

If you make a slip cover/pillowcase for whatever type of rigid material you chose, it can be pushed into place in the bottom, but removed for washing.

Cover the cardboard with a sleeve and leave one end open. Then you can slide the cardboard in and out, as needed.

You can get very inexpensive plastic place mats that can be cut to the size you want, too. The sleeve technique works for that, too.

I just use the plastic bags in the store and return them for recycling. I would rather spend my time making quilts.

Foam board is great too. Cover if desired and make it removable

CurlyQ - are you using a particular pattern, size for your bags? I would also like to make some, especially for my daughter for her big shopping trips for groceries. She has four kids and needs lots of food often. A bigger bag with a flat bottom would work best. One that sits flat when putting things in.

Thanks.

WalMart has vinyl placemats for $.88, which could be cut to size and removed for washing.

I just make a casing, sort of like a pillow case, that can be removed from the cardboard. Remove to wash or replace the cardboard as needed.

Just don't sew it into the bottom of the tote; just place them in the bottom of the bag. Once items are on top of them they won't be going anyplace.