I have an index card where I write and scratch off possibilities for extra GS or clay.
Skulls, bottles, vases, and books are my go-to. Stuff to put on shelves later on.
Grubs/giant maggots are also a good one along with giant egg clutches and sacs. The eggs end up being nice objective markers.
Bags, backpacks, and satchels also get a lot of play for extra clay. Usually, though, I want these custom fit to a figure. But they can go on bases and shelves without that.
Tools are another good one. Hammers, wrenches, screwdrivers, bolt cutters, various types of saw, and on and on. Tools are nice because you can make a variety of little bits as opposed to generic thing rinse-repeat, if that's the current mood.
Office gear is also good if you're doing modern terrain. I dislike empty desks, so computers and notebooks, and supplies help liven up the scene.
The last one is baskets and bags, either empty or full of food or other supplies. Good generic, all-genre fare. Who doesn't need a sack of potatoes?