1. Place item (food/water) in hand.
2. Place random object on the floor and make sure its visible in Tab screen. (can opener for example)
3. Select eat all food on the item you have in your hand
4. While the item is being eaten/drunk drag the random object (can opener) to hands.
5. The character will finish eating/drinking and the food/water will be on the floor at 100% and you'll be hydrated or energized. This can be done pretty much forever, the success rate is 100%.