Every action that you do and every task that you wish to perform takes energy. It recovers 1 unit every 5 minutes real time and can also be recovered by trading in food units for meals.
3 kinds of Energy Drink will restore energy by using them in your inventory. These are usually received as gifts from friends. It isbetter to hang on to these, you need to collect 25 for Liz in Stock Till You Drop.
These promotional items are acquired infrequently and can't be bought or gifted most of the time.
If you run low on energy, or have extra food on hand, you can go to the Energy Market and purchase Energy Packs.
This is the primary use for food collected while farming, as well as a way of making sure that you can complete missions that are time sensitive, without having to wait to charge your energy. Some missions also require collecting certain amounts of food.