Potatoes/sweet potatoes/squash-save the peels in the freezer for broth.
Herbs- parsley, sage, rosemary, thyme, oregano, basil, cilantro. Just keep in mind what kind of soup you plan to make. If you want a basic broth, leave out the herbs until you're actually making the soup.
There are a few items I don't use. I try to keep out seeds, so I don't use the cores of things like peppers. Also I skip the skins from eggplant which can make the broth bitter. Some recipes suggest not using cabbage or asparagus, but I've used both and the broth is still fine. They're just strong flavors. You can use apple peels, but the broth will be extra sweet.
Here's the vegetables straight from the freezer. Onion, carrot peelings, celery parts, the stems from turnip greens, some summer squash and the peel from a winter squash, and the greens from some leeks.
All the simmering veggies.