This is definitely more difficult. Setting reminders, taking advantage of public gyms (if available), getting outside for a hike or walk and YouTube workout videos are all great ways to keep you active while in a less ideal surrounding.
I usually don't travel, so it's not really a problem for me. You can still go for a walk/run, there are no restrictions.
Well, usually I'll stop at a hotel. And the hotel has a gym so usually I'll use that. But if there is no gym I clear out the space around me and use what I can. Like if I want to lift weights I'll find something heavy. Simple!