You can usually group your items in 4 different categories: cans, fragiles, produce and meat. Usually none of these categories can co-exist in a single grocery bag peacefully without one destroying the other.
In case your wondering the reasoning behind grouping, it has to do with cross-contamination in most cases. Raw meat items cannot be placed with exposed fresh produce. The bacteria from the meat might contaminate the produce, and vice versa. Also, fragile produce items such as apples and grapefruits should be bagged separately and handled with care. Furthermore, you should never place wet items (such as freshly watered celery stalks) with that outrageously priced Hallmark card the customer bought for obvious reasons.
By grouping them, you can begin the next step...
And yes, that is a bottle of Jim Beam's finest bourbon in the picture in case you're wondering.
The golden rule of grocery bagging: Heavy items on bottom, light items on top. It will save many problems with the customers. Eggs do not belong below 5 cans of canned chili con carne. Eggs don't even belong in a bag containing cans, period. 6-8 cans can fit in one bag, and remember to place the bread and eggs in a separate bag.
A ordinary order would be bagged like this:
One bag with 5-6 cans of food
One bag with a dozen eggs on the BOTTOM, and one loaf of bread on TOP
One bag with a variety of produce
One bag for all meat items except poultry (separate poultry from red meats)
All fridge packs, cased goods, and bags of pet food should be placed on bottommost shelf.
Gallons of milk and anything with a handle can be simply placed back in the cart without a bag unless requested.
The final destination your nicely packed bags of fine grocery items will go as they exit the store. Remember to place that bag of canned chili con carne on the bottom of the cart, and place that bag of eggs/bread on top. The golden rule still applies if you haven't noticed.
Also, remember items such as those fridge packs of Coca-Cola should go on the bottom shelf that are found on most carts.
Step 4: A "what If" - What to Do When a Customer Wants to Return Their Items
This sucks. All those nicely packaged groceries are going back on the shelf, because all he has is $40. Unpack the groceries, place them in a nice box and continue going aisle-to-aisle returning those unpurchased groceries. The joys of being a courtesy clerk is never ending....