I use a trackball, so as such, I don't have scroll wheels.
Where in the config can I change this and select a key to use, or am I, pardon the pun, hosed?

Hi @antiwesley,

I added quick and dirty implementation of this feature in my public fork of this repository, and it seems there are no issues with cycling through items using keys only. You may find the modified source here (works on 1.16):
GitHub: Travellers Backpack Fork: no-scroll-weel

I modified it to use with "controllable" mod using a PS4 controller. And it does the job.

You can build it from the fork or just download it here:
TravelersBackpack-1.16.5-5.4.3.jar.zip

To cycle through items and hose modes, press the configured key. It will switch to the next tool or hose mode (no mouse wheel required).

https://www.curseforge.com/minecraft/mc-mods/travelers-backpack/files/3495735