This is the simplest food hack that comes to my mind first. It was suggested by my uncle when I used to travel by train mostly or sometimes by bus to Hubli, Karnataka. I did my Bachelor of Homeopathic Medicine & Surgery (BHMS) from Hubli. He said this was the best food while traveling! And rightly so.
This is another quick food hack if you don't have any options. You take rice and mix curd. You can add a little bit of water and a pinch of salt. Did you know it is Sunnah [practice of Prophet Mohammed (peace be upon him)] to have a pinch of salt before and after every meal. And I found out recently that the Turks eat curd after every meal to digest it! I definitely follow both the above practices! Hey, and you can add bananas, sugar, pomegranate as top-ups to the curd rice.
Besides the ones listed previously, you can also try out the above-listed easy food hacks. Always try to eat healthy (all the more better if they are organic) foods like milk, jaggery, honey, etc. for a fruitful and productive life. And if you still feel low, check out how Homeopathy can help you out here!