the only "self-check-out" system I have ever liked is:
- I have the store app on my phone.
- I scan the items with my phone app as I grab them off the shelves.
- I then tell the app, "ok, i'm ready to pay for these"
- it runs the charge digitally.
no waiting in a queue,
no 'place the item back in the bagging area',
no stuffing bills into slots,
no 'follow the instructions on the pin pad'.
I'm already done!