When I travel I always tried to carry some food that could be easily eaten in a bind. I also kept water with me just in case. Good for the aiport, train or bus station, or bus breakdown along the way when there is nothing around.
I would carry alomst anything that kept for a long time. Candy bars are easy to find and can give you some calories to make it through. Granola bars are better for you and give more nutrients. Military MRE rations are best all around but taste bad.
I always put these on my carryon bag or top of my pack for easy access. Canned meat or vegtables work in a bind too if you have limited shopping around. I find this is also handy if you fall ill for a couple of days and need something to give you energy to get to a doctor or pharmacy.
This is also good for those “unexpected camping” nights when you are forced to fend for yourself in some random small village in the middle of nowhere.