To add a data point regarding self checkouts (I'm wondering if anyone else experiences this). Often when I'm waiting for a human checkout, I'll see the snacks and drinks, and throw one on the belt. But when I go to the self checkout I'm so involved with "a job to do" (that is, doing the job of a checkout clerk), that I've never considered adding a candy bar to my purchase. It is only after I've completed and paid, that I think "Gee, I really could have used a Snickers". But then it is too late, I've already paid and there is someone behind me waiting to use that checkout machine.