In kindergarten, my class planted seeds in empty half-pint milk cartons. The plants -- I think they were lima beans -- have been composted back to the earth, but I remember the lesson even decades later: A lot can be done with empty milk cartons.
Here are a few ideas that I have collected from a variety of sources:
Woman's World (Nov. 21, 2006):
* Oil collector. Keep your kitchen drain free, by pouring grease, oil and other gunky food by-products into an empty milk cartons.
*Picnic ice-pack. Clean out an empty carton. Fill with clean water & freeze the cartons. Bring the frozen block along on your picnic or tailgating party. It's a good way to keep your food cool and when the water melts, you'll have instant cold drinking water.
Personal note: During Hurricane season, we stuff our freezer with containers filled with water. The same reasoning: The frozen blocks keep our freezer cool during power black-outs and the melting ice becomes a valuable source of drinking water.
* The pooper scooper: If you have a pet, you can imagine how a plastic milk jug can be used for this purpose. Hint: Remove the bottom and use the rest as a shovel.
Source: Woman's World
Frugal Japan has very creative uses for milk cartons, including a drawer organizer, disposable cutting board and a microwave baking container.
From Reader's Digest: instant bowling alley, portable ice packs.
Milk carton crafts for kids
The Frugal Duchess Boutique