rice example:
1. place any item (item x) on the ground
2. open inventory so you can see item in vicinity
3. right click rice in inventory and 'eat all'
4. when the animation triggers drag item x from vicinity over the rice
5. you will continue eating the rice, item x will be in your inventory, rice will be on the ground and still at a 100% (or w/e value you started with)
6. repeat endlessly
the same steps can be used for cans, fruits, drinks, saline etc.