Supposing a man buys a box of food at a clearance event where signs are posted that say "All Sales Final." When he gets home, he discovers that it is a week past its expiration date. Is he just out of luck?
Best-before dates are optional consumer advice and are not legally enforceable or required, at the federal level. An exception is infant formula, where a date is required by law. There do not appear to be any states that require food to be removed at or after any of the various "pull" dates, but there is some variation in whether items have to have a date on them (NJ requires that fluid milk products and bottled water yes that is right bottled water have an expiration date). It is still legal to sell expired water. California law does restrict post-date sales on OTC drugs and baby food, but not generally. California's legal return policy Civil Code sect 1723 which requires stores to take back goods also restricts returns of food and "all sales final" goods:
This section does not apply to food, plants, flowers, perishable goods, goods marked "as is," "no returns accepted," "all sales final," or with similar language, goods used or damaged after purchase, customized goods received as ordered, goods not returned with their original package, and goods which cannot be resold due to health considerations.