The Amazon fresh near me has a buggy with a bunch of cameras and a scale on it. When you drop food items into it, it's automatically added and weighed. When you push the buggy to an exit line it checks for any errors then emails you a receipt.

If you're wondering how it detects the produce, produce in the US has tiny little stickers on it or at least a PLU code where its sitting. You enter that 4 digit code and it gets weighed.