Fitness

Buying a resistance band can be great to fill in the gaps between hotel gyms. Doesn't need to be anything fancy. Something portable that you can travel with to add resistance to bodyweight exercises. Only other tip is to superset your workout, mainly for the time benefit. I travel a good bit for work and it's amazing how I lose track of time and skip workouts due to time limitation.

Are you in hotel rooms the whole time?

Body weight squats done with intensity can be killer. Pushups too. Suspension trainers are decent, but the core needs to be squat, push, pull.

If you're really skinny working on stabilizers will be very worth it, especially on your shoulders. Bands will be good for that. Work that rotator cuff. Pushups on the suspension trainer.

When you get access to gyms pulling movements are important because those are hard to do with bodyweight stuff. That's also where suspension trainers will help.

You should be able to find an actual program somewhere. There is a market for what you're looking for so doubtless someone's made it.

How about Freeletics? Even though I never liked it that much, but the idea behind it is fairly okay for certain circumstances.

Unilateral exercises like skater squats, pistols, 1-legged RDLs, etc can help you maintain some strength/muscle and can be done anywhere. Inverted rows if you have a desk or table handy.

I travel often for work. I bought a Trx to use in the hotel room.