For dry goods I don't even look at total price, I look at price per weight (wet goods, same but volume). It's almost always lower the more I buy. I'll buy the largest quantity I can consume before it spoils.

Off the cuff I'd say I save about 20%, and buy a few hundred pounds per trip. Probably saves us amongst a family in the vicinity of $1000/yr. This same concept extended to all other non-food consumables.