...Other than salt and pepper
For me it's cumin. It's one of the few spices I buy in bulk and actually use up my supply.
In the winter it may lean towards cardamom thanks to copious amounts of chia.
Some top ones for me: MSG, Chicken Bouillon, Smoked Paprika, Thyme, Garlic powder, and finally, controversially, bay leaves.
MSG goes in basically anything. If it gets salt and pepper it's probably also getting MSG for me. I do a lot of chicken, and whenever I do I'm almost always adding some chicken bouillon to add some flavor to it. I really love Thyme, and find myself just adding it somewhat randomly to things. Smoked Paprika is a perfect flavor that's so unique, I add it to anything I want to have a bit of a kick, like chili, ect. Not that it's like spicy or anything, just it adds a little something to those dishes that you can't really get elsewhere. Garlic powder is an all around great utility, and I tend to "dump" this stuff on things.
Last but not least, Bay leaves. I swear, I'm like the #1 consumer of these things. I throw them in anything. Anything savory with a decent sauce/soupy base is PERFECT to add a bay leaf to. If you use em often you can really taste the difference, since fresh bay leaves really pack a punch in flavor.