For your benefit:

• If you know you're going to freeze something (like meat, fish or bread) anyway, ask the grocer if they have some still frozen from the distributor. Re-freezing isn't recommended, and stock often comes in frozen, then the grocer has to thaw it to put it on the shelf.
• Bring your own grocery bags. Reusable bags are sturdier and can hold more items, often with better insulation than paper or plastic. Also, bring a variety of bags: squarish bags are better for dry goods and boxy items, while simple sack shapes are great for holding produce that fits loosely together.
• Always clip coupons for items you know you're going to buy. Why not?
• Learn to watch for items on sale (perhaps a brand that's new for you) and items that may not be on sale much longer. Pay attention to sale flyers, signs in the store, and sale tags on the shelf.
• Pay attention to your cashier. You might be able to catch a mistake she makes if you just keep an eye out. Cashiers are human, and are usually happy to correct a mistake or make sure you get the right price for an item.

For the sanity of grocery employees:

• Be patient. If you have a question or need assistance, the grocer is usually happy to assist you, but it may take time to find an answer to your question, or to find the right product to fit your need. Not all employees are experts, but many have more knowledge than you may expect. If you really need an answer, stick around to hear it.
• Make an effort to bag your own groceries, unless someone has already started bagging them for you. And vice-versa, if you've started, and a bagger comes along to help, let them!
• Another note on bagging: trust the person who bags your groceries. Saying something like, "I'd like the cold items bagged together," or, "I have two separate orders," is usually clear enough. Any bagger worth his weight will immediately know to pack like items (dry goods, produce, prepared food items, frozen and dairy) into separate bags. Don't hover around the bagging area shouting specifics. It slows down the process and backs up the line behind you.
• Put your grocery cart back where it belongs! It DOES belong in the line of carts inside the store or in one of the "cart corrals" in the parking lot. It does NOT belong:
  • on the sidewalk
  • in another parking space
  • in a planting bed
  • in an outdoor seating area
  • in a line of other carts ALSO in a wrong place
  • at a neighboring store