I worked as a bagger in a commissary once. For a few weeks. Turns out that the tips aren’t really worth it (commissary baggers are not paid by the commissary, they depend on tips alone). But yeah, we were taught to bag.
You can put no more than TWO layers of canned goods on the bottom. And canned goods belong ONLY on the bottom. You can put more stuff on top of the canned goods, but only very lightweight stuff like toilet paper or chips.
Don’t bag nonfood/poisonous items with food, particularly produce. This means that you don’t put the dishwashing soap in with the grapes. MOST of the time the soap won’t leak…but there’s always that chance. It’s even worse if it’s furniture polish or something like that.
The only thing that goes on top of eggs is bread and potato chips, as they won’t crush the eggs. Don’t stand the eggs on end, as they might crack.
Bag the cold stuff together! If you have more than one bag, put all the frozen stuff in one bag, all the refrigerated stuff in another. Some of our customers drove quite a distance to get to the commissary, and this was in Las Vegas, so bagging the cold stuff together helped keep it cold longer. Plus, it was easier for the shopper to unload at home.
Light bulbs go on TOP of the bag, not the bottom.
As you can see, most of this is common sense if you stop to think about it.
When we shop at the “bag it yourself and save” stores, we generally follow these rules ourselves. Oh, and we bag all the bathroom items (toilet paper, soap, shampoo, female hygiene, etc.) together, which means that we can just take that bag or bags into the bathroom to unload it.