[etc.]

I would see if I could steal a roll of the paper that they put into thier recept printer.
That would make things a lot easier if they have some sort of print on the back (Never been to walmart, I live in the UK).

Do they have a store on the internet, you could say that you bought it from there and forge a "Conformation of Order" email of something.

I don't know much about your situation though,
what is the product??