It really depends on the means of travel;
Car: get an inverter so you can plug your Inogen in and charge it, run on battery only when you can’t have it plugged in.
Air: some airlines have electrical plugs to plug into. And always carry the plug in with your Inogen.
I bet if you needed to plug it in somewhere like a restaurant you could explain and they would most likely accommodate - I had to do that a few times with my wheelchair.
My husband uses an Inogen and I have inverters in our vehicles.
I don’t use it but one of my closest friends always had to have it with her 24/7 so since we were tofether quite a bit I learned. First, it will depend upon your mode of transportation and the length of time you are traveling. By car and for short periods of time we kept extra canisters in the back seat of the car. If she was going to be somewhere for any period of time she would make arrangements to have oxygen delivered to her temporary location. On cruises you would make arrangements to have oxygen on board for the length of the cruise.
I would say that preplannimg is number 1. You have to notify a cruise line well in advance and I believe you have to have a letter from your PCP stating yiur need for supplemental oxygen. I know you can fly bur there are requirements because another friend wss telling me her pulmonologist had a booklet of flights with regard to altitudes for each flight and he helped her plan a flight home to visit her family. I would suggest to try Google for information on companies who deal with providing supplemental oxygen. I am sure you could also find much needed information there.
It will be easier if you are in one country because you may have to have inverters to change from 110 to others. I would start with my oxygen supply company and any transportation companies such as airlines. Also don’t forget travel agencies they are well acquainted with needs.