Buy loose mixed greens. Avoid the temptation of the pre-washed packages of lettuce unless you want to eat three or four consecutive servings. Avoid the temptation to buy those small, loose servings of crumbled feta. They're usually not as fresh as the blocks. You may have to dig, but find the smallest blocks of cheese they have.
Crackers are a problem area.
Unless you eat the entire sleeve, they go stale quickly because of poor wrapping. If you buy Ritz, store them immediately in an airtight container. Ask the butcher to cut roasts or chickens into pieces big enough for one meal. For more personalized service, go to a small butcher shop. Stay clear of processed convenience foods whenever possible.