Keep all receipts so you can take back extra boxes (:
Or you could order them online as you need them and keep the money saved... Babies grow fast my son was in size ones for a weekafter he was born then size 2 now were in size 4 and he just turned 9 months old been in size 4 since january
You can always just exchange the diapers if you need a different size I never had a problem even without receipts.
I agree with exchanging or you can just put money on a gift card so its saved up and you dont have a lot of boxes everywhere.