Push-ups, planks, bodyweight squats, and lunges can be done literally anywhere. But pull-ups require something to hang from, and that won't always be available.
If you travel a lot, you know that it isn't easy to find a gym. If you're lucky, the hotel you're staying at has a gym, but you'll have to be real lucky for that gym to be equipped with a pull-up bar. But there's still a way you can do pull ups. All you need is a door and a couple of towels.
Just follow these steps.
As a bonus, towel pull-ups really hit your grip and forearms hard.
Find yourself a set of towels or rags made from a thin material and keep them in your suitcase. And never skip your pull-ups.