Like others, we take care of maintenance items. I've sanded, painted/varnished when I could. Bruce has a gas-powered generator and upon occassion would use it to run power tools (Amphora's engine room was quite roomy!). Bruce made alot of our accommodations while underway on (e.g., bunks, cabinetry, shelves, & handrails for our boat).
Dry days take care of the laundry. I constantly clean and make sure items are properly stored and check portholes and hatches and seacocks... and follow behind Bruce to make sure his tools don't go overboard.
Curl-up somewhere with a good book (Bruce on the Manawa Nui
, a 1941 55' Ketch).
Think about what to make for dinner.
See what the neighbors are up to.
Test rattlings (which I made underway). Or perhaps, listen to a little mood music (Bruce and his sons play, I don't.)
Bruce and I take turns reading to one another or if it's just the two of us? Other things.
When the weather starts to turn ugly? Make a pot of most excellent coffee and prepare and store a few easy-to-keep-down
snacks and/or meals just-in-case the galley needs to close. And again, check that items are stowed and hatches/portholes are buttoned up.