When I go grocery shopping, I often stock up on sale items, such as frozen vegetables, canned tomatoes and boxed pasta. I also like to treat myself in the produce aisle, buying fresh pineapple, carrots and melons, whatever is a good deal.

But to be honest, my husband and I usually don’t eat an entire bag of baby carrots or a whole cantaloupe, so I end up tossing the leftovers in the trash.

Earlier this winter, my husband defrosted our iced-over freezer, and we discovered more than...