I also worked at a "mom & pop" grocery store bagging groceries, and got tips. (Well, it also happened to be my mom & pop, but that's not relevant)
I don't think they do it anymore, but back then the bagger would not only bag your stuff but take it out to your car and load your car.
Not everyone tipped. Customary low tips was just the change they got back from their order, 25-50¢. A dollar was also common.
There was one guy that worked there that had been a bagger for many many years there, he practically knew everyone's name (all the regulars) and how many kids they had and everything else and basically had a really good relationship with hundreds and hundreds of loyal shoppers.
He easily made $40+ in tips per hour, plus whatever he was getting paid.
Anyway, this whole story took place in like 1992?ish. That guy no longer works there, and everyone prefers to take out their own groceries to their car now.