I store 90% of my shoes in the original boxes that they come in.
I always put the sales receipt in with the shoes.
If for some reason I need to return them or question how old my workout shoes are, I have the receipt right there. No digging through a mountain of other receipts looking for it.
I also have done this with books that I purchase – especially cookbooks – I put the receipt in the back of the book. Sometimes I just want to know how long I have been using that cookbook.