There are some things that are easy enough to figure out when they expire—like eggs, milk, and food with clearly marked expiration dates. These things described below do not have listed expiration dates, but will lose effectiveness through time.
Natural loofahs and sponges can begin to breed bacteria in only a couple of weeks. Plastic mesh loofahs are safe for a little longer, around up to 8 weeks. So rinse and dry your loofah after every use and replace natural loofahs every couple of weeks and plastic mesh ones every other month.
Ripe potatoes should be good for 2 to 3 months. Do not eat them when they are green—this means they are unripe or sprouted—this means they are overripe. Keep your potatoes in a dark and cool place. If you really want to make use of your potatoes, check out these food made better with potato chips.