If you're like me you can taste the difference between a beverage that has just been opened and one that has been opened for several days in the refrigerator. Orange juice in particular loses that appealing "just opened" taste after only a day or two. Since I don't always finish off a carton within a day or two after opening it I often experience a noticeable and undesirable change in taste. This happens with many types of beverages and since I usually purchase high quality beverages I dislike having to discard something because I can no longer enjoy its taste.
My solution is the Stay Fresher Longer Dual-Chamber Beverage Carton. Looks and feels the same as any standard half gallon carton (could be made available in other sizes as well), but has an internal divider(s) which create two (or possibly more), completely separate chambers. Chambers are only opened as needed. The divider may actually need to be placed diagonally (not as shown in the drawing), to prevent tipping when one side is empty and the other is full. More creative divider arrangements could easily be designed to allow for better stability while maintaining equal volumes.
This multi-chamber idea might also be a great delivery method for various mixable beverages such as mixed drinks. Also, certain prepared food kits sold in grocery stores contain food items that must remain separate until they're ready to be cooked or otherwise consumed. There may even be applications outside of the food markets.