Left handed trackball (Elecom). Sits to the left of my Moonlander while my vertical mouse sits to the right. Not only is it convenient, as an old school Diablo player I get to tell people I duel wield.
I also have a cheap X-Pen graphics tablet that I use for ‘white boarding’ on zoom calls.
Almost forgot I also have a usb wireless numpad that I pair with a usb hid remapped on a pi zero to make hot keys for frequent actions.
I have an XP-Pen as well. Works great in Linux. I'm still amazed at how high quality these non-Wacom tablets are today. I had one of those cheap 6" Wacom Graphites back in the early 2000s and that was the best you could get. My XP-Pen blows that thing away. Still haven't found a great place to put it though. I'm just stashing it off to the side but it's awkward moving it around all the time.
If you're on Linux, Gromit-MPX is a great companion app to annotate anything on your desktop. https://github.com/bk138/gromit-mpx