Upon searching for about three seconds the next day I found about seven apps that did that. Reviews for a few are here.
I think I might buy the "Grocery Gadget" one - it looks like it does a little more than just create a check off list and I like the idea of creating several lists for different stores...and even putting some pictures next to items for the weird stuff that's hard to find (Asian Market, anyone?).
Plus, I walk around the store with my phone anyway - usually obsessively refreshing Facebook - so at least I can use the phone more constructively while shopping. If I actually had music on my phone (I use my Pod for music, phone for everything else) the phone would be a PERFECT gadget to bring food shopping as I usually like to put headphones on while I shop so no one talks to me. Maybe I will download a shopping playlist onto the phone just for that purpose.