@greghiggins @rnv Lists, mostly. To-do lists & reminders; words & etymologies I want to research. Grocery lists, too, sometimes. Also, scratch paper for calculations. (I have the sublime PCalc on all my devices, but I honestly almost never use it, except sometimes for really huge problems, and of course for the About screen game. If you know what to type into a calculator, you probably already know how to do the problem by hand.)
We just bought a house a few months ago, so the last two Field Notes are full of things like: how many light fixtures, outlets, and switches there are in every room; and how many windows (and therefore how many curtains & curtain rods we’ll need). I have a larger graph notebook with a detailed floorplan of the house; FN pages are too small for that sort of thing.
I also use reminders and lists on my computer/phone (e.g. Due, Things), but I'm all about redundancy: plenty of what's on paper is on my computer, too.