1. Translation
2. Maps and Directions
3. Ticketing Services
4. Ride Hailing Services
5. Weather
6. Camera
7. Making calls from anywhere to anywhere
None of those are necessarily what people think of first when they hear "smartphone", but without them traveling would be a pretty difficult experience. I know firsthand, because I traveled prior to having these things. I had to deal with the expense policy at work trying to figure out how to get and handle cash in multiple countries so I could pay for a taxi and risk getting ripped off, or buy a train ticket. I had to carry around a phrase book and hope my pronunciation was close enough to get things done without offending anyone. I had to deal with paper maps, and get lost, and hope I made appointments on time. I had to roll around a wheeled pelican case with camera gear to get any decent photos, taking up precious space and making me stand out. And for the weather, well, I just looked outside and hoped I brought the right clothes.
I don't use social media, except Hacker News (if that counts). I don't really do any of the things you probably think of when you think of smartphones being problematic, but having this devices has made my life immeasurably better. So much so, that it's probably the most essential thing in my travel kit.