I'm actually quicker packing my groceries into my own bags than if the cashier does it.
I haven't seen an actual bag boy in a long long time, and most of the cashiers have no idea how to pack a grocery bag. They are really slow and do it all wrong. There is a system, you know.
not too many cans or bottles in one bag to avoid breakage
produce together, heavier items on the bottom, not overloaded
meat separate
eggs/bread/bananas on their own or on top of something else- not squished down the side.
cleaners/soaps separate
frozen items together