Useful when you are hungry

The most useful things when you are hungry is food.
The reason is our body need it.

Long time ago, I saw some documentary films. Some of them were talking about our body need. Acutually, our body needs some sources to allow our body moving. When we are in space, if we can't carry a lot of food with us to travel a far far planet. In according to our body need, we can produce pills to tackle our natural need. However, our structure has a process to digest food and absorb food. Our stomach will get into hungry and will secrete gastric juices to digest food. If there is no food to digest, it will hurt our stomach and hurt our health.

So, the most useful things when you are hungry is food.