A 2-in-1 Chromebook (folding form factor) with a stylus and Crostini support for Linux apps may serve you well.
I've been fairly happy with my Samsung Chromebook Pro on BART in the SF Bay Area -- in tablet mode I watch lectures using VLC, read PDFs using Xodo, and take handwritten notes (often while splitting a screen with one of the former apps) using Squid. And I can always flip it into laptop mode and run Linux via Crouton for Vim, Octave, REPLs, and QOwnNotes. (I use my Android phone to create a WiFi hotspot when needed for email etc.) Everything syncs up over Dropbox using Dropsync. The aforementioned Android apps all run quite well for me.
(I probably wouldn't recommend the Samsung CBP right now - it's a bit old, and Crostini support has been rumored for a while now, but never materialized. Especially if you want LTE. But Chromebooks are at this point pretty good as Linux and Android machines, and the styluses work well for note taking.)
No real OS but I use an iPad pro 11, mostly because it never fails to work (including it’s excellent battery life and fast charging). For a real OS; I am still looking; I found the surface pro annoying after a while (and the one I had had miserable battery life). For now only intentionally hampered devices work for me in commute; either too small (Pocket or Pandora) or limited OS (Android/iOS). All other I tried are either too big or crap battery life; even the big winners like Lenovo X* or T* or macbook pro really do not have more than a few hour battery for my workflow.