Select the product with the least packaging in the largest convenient size. If your favorite brand is the one with a bag inside a box inside a plastic overwrap, complain to the manufacturer. Often you'll find a toll-free number on the package asking consumers for their comments. Your opinion counts. Do as the Europeans do, carry things home from the store without a bag, or use your own.
Most items are already over-packaged.
It's silly to put a box of bottled aspirin or a loaf of bread into another wrapper. Avoid single-use or disposable items. Give up paper towels and use a sponge or rag to wipe up small spills. Cloth napkins can see a lot of duty before they're relegated to the rag pile. Buy refillable pens, razors and lighters.