Universal store card
All of the above problems plus the bother of spelling out an email address at the till.
Just a spur or the moment thought...
Could some sort of independent and universal store card work? Whoever ran it would end up having a mountain of your data, but maybe the receipts could be encrypted in two forms, first so only you can see it and secondly by the store account so they can see it (or is that even needed?).
Maybe something like Lastpass, or whatever, but for receipts and comes with a physical card (or contactless) which can be bopped after, or somehow with, your payment.
Or maybe it would be easier to somehow combine the full receipt with the transaction to your card provider.
I don't suppose this gets past the security guy problem, unless there's an easy system to call up your receipt from just another contactless swipe at the store.