I have, a few times, had a campsite that had only a 50 amp service - only! Not even a 15-20 either. It's those times, I'm glad I have to 50 to 30 amp dogbone.
For the OP: yes, pick one up and keep it tucked away in your camper. About the time you swear you'll never use it, ... bingo! You're going to need it!
Plus.... If you are on a site that has both 50 and 30 service, you can always run the 30 amp to your camper, plug in the 50 to 30, and then get a 30 to 20 plugged into that. You can run extension cords everywhere!
That's how I was able to plug in ALL of this for a Christmas in July contest (and won first prize!)