What tools can you not live without when GMing around the table?

I tab back and forth between One Note, which holds my notes; a browser on Archives of Nethys, and Pathbuilder 2e's "Encounters" feature.

Pathbuilder Encounters is probably not the best most full-featured encounter management tool out there, but it automatically syncs with my players' Pathbuilder characters, which I find brilliant because I can see all their stats and character sheets. Lets me see the difficulty of encounters as I add monsters, as well as automatically roll all their initiatives, manage HP, etc.

Biggest negatives are that there's no way to enter custom or third-party monsters (at least that I know of), and that changing initiative order (e.g. when knocked unconscious) is an awkward manual process.

I use Trilium for my notes (it's similar to Obsidian MD, but open source, and WYSIWYG), pf2easy for quick references, and custom soundboards and Bluetooth speaker for ambience.

I picked up some "gold" fantasy coins to use a physical representations of hero points, some silver ones for focus points, and have printed off my own spell cards using pf2easy's spellbook and some cheap card stock. I had been using coins for spell slots for a bit, too, but a less generic option was required after a few levels.

The Advanced GM screen has been a great resource during sessions, too.

I don't currently have a laptop, so what I find invaluable might change once I get one.