I used to travel a lot and found that almost every hotel I stayed at had a gym with weights, and some even a cage on which you can do pull ups. Barring that, you can buy a pull up bar that fits into a nylon bag for travel. It's not cheap though:
https://www.amazon.com/All-one-Stand-Alone-Pull/dp/B001KUURTS/
I used this model for nearly five years and never had any issues with it. Later I invested in a fixed pull up tower that also doubled as a bench for presses when we bought a house that had a dedicated gym space for me.
I have this. It rules. You can set it up anywhere with no tools. Plus, it allows you to go inverted, which you can't do on a door mounted bar. No kipping though, as the legs aren't long enough to keep the rig upright.
If stability is a problem with that rig, this might work for roughly the same price: http://www.amazon.com/All-one-Stand-Alone-Pull/dp/B001KUURTS. Adjustable height, and they can make it shorter at no extra charge according to the Amazon Q&A. It wobbles, though. See review: https://www.youtube.com/watch?v=Nih7cJVe_Ro Word of warning, you can really go down the rabbit hole looking for the "best" chin-up bar. I spent weeks researching before deciding on a rig even more expensive than the one above, but my favorite places to do pull-ups are still (1) outdoors at a park or (2) on my $20 doorway bar I've had for almost ten years now.
I bought a folding pull up bar from Amazon, which works well enough as long as it is placed on a non-slip surface.
It might look flimsy but it is made of lightweight and extremely strong aluminum.
I switched to this unit because it could accommodate bench and squat presses:
It is not portable, of course, but I have a permanent gym downstairs and it saves on space.