I learned to not waste juice by filling the kids’ reusable bottles — pour in the same amount of juice that comes in a juice bag, about 6-8 ounces. Even then, the kids were coming home with juice to dump out, so I cut back from the 6 ounces. But they should really be drinking water when they get a chance at breakfast, during the day, and after school. At least once a week I just fill the bottle with filtered tap water instead of juice. It’s practically free and they need to drink more water anyway. I’ll look into a comparison of tap versus bottled for another day.
Switching to filling your own bottles will also result in cost savings because after the initial bottle purchase (about $3 each), the juice is much cheaper to buy in large bottles. On sale at the grocery store you can get 64 oz of 100% juice for $1.00 (no added preservatives or colors).