Depends on how you define "comfort zone". There are things that make me physically uncomfortable, or cause actual pain, that I do anyway as an unavoidable part of travelling. There are things that make my psycologically uncomfortable, the usual meaning of "confort zone". Finally, there are things that used to make me psycologically uncomfortable that I've managed to get used to. Some examples from each:
Long plane flights. Even with stretching exercises, I need hours afterwards to recover.
Steep hiking trails: I love the overall experience, so I just learned to live with the burn.
Staying somewhere sketchy, both the lodging itself and the surrounding neighborhood. I remember one hostel where I slept fully clothed with my pack as a pillow because I was afraid of being robbed.
Sketchy areas at night: I've had to learn how to spot potential trouble, and steer away from it, but they still set me on edge. I suspect this is actually a good thing.
Driving isolated dirt roads: I'm always worried I'm going to break down or get stuck and not be found for days, if ever. I now take them slowly and carefully, and think about why I'm there in the first place
Gotten used to it:
Sleeping in a hostel dorm: At first, people kept me up and I worried about fitting in. Now I bring ear plugs.
Less than perfectly clean accomodations: Bugs and germs and dirt, oh my! I learned to take precations (flip flops to avoid athlete's foot, bug spray, netting, etc) and finally got used to it.
Street food: More variety and cheaper than restaraunts, at the cost of potentially getting nasty germs. I learned about what to look for (ensure its well cooked in front of you, for starters), and got more comfortable as I got more experience.
Whitewater rafting: I learned I could handle this one the hard way, by falling in and having to swim. The experience was important enough I wrote a blog on it.
Heights: Many hiking trails run very close to cliff edges and other areas with long views. I spent much time explictly feeling the security of my holds on the trails while staring at the views. The most extreme example was Angel's Landing in Zion National Park.