I hate supermarkets so usually get in and out as quickly as I can. Often that means not getting some items on the list. I mean sure I've occasionally picked up stuff that hasn't been on the list but that's usually because it's something that should have been on the list but was forgotten about (eg milk or eggs - basics that get used frequently in a family home). However the times I walk out not buying stuff on the list far outweigh the times I've walked out with additional stuff that wasn't on the list. So I've never understood why people need such complicated systems to reduce supermarket spending like those described in this thread. But I guess everyone is different and perhaps some people like shopping and are prone to impulse buying?