Grocery store sales are fantastic until you arrive and discover the shelf is empty. A rain check is a written promise from the store allowing you to buy an out-of-stock item at the current sale price at a later date. Most major traditional supermarkets like Publix and Kroger gladly offer these slips at their customer service desks upon request. Utilizing this old-fashioned retail tool is a brilliant way to lock in a low price without having to chase the delivery truck. Let me share six smart rules for using rain checks to protect your weekly family grocery budget.