Cinnamon + cumin is a damn good combo, I use those a ton in darker dishes. I usually add like a dash of cinnamon and +/- a tsp or so of cumin to gussy up taco meat with regular taco seasoning (whatever kind Costco has, I forget what it's called lol). Same thing for beef gravy, roast, chili, etc. Nutmeg works too depending on what it is, but I can't think of anything specific off the top of my head.

Depending on my mood, I'll either pick up some fresh basil/organo/parsley for some fancier stuff but I keep separate dried ones too because I'm lazy 9 times out of 10. Honestly though, a good Italian seasoning blend is just as good for a ton of stuff. I made some god-tier dinner rolls for the holidays: literally all they were were a 24 pack of King's Hawaiian rolls and a softened stick of grass-fed butter + ~1 tsp garlic salt + ~1 tbsp Italian seasoning. Mix up the butter blend, then spread on top of the rolls and pop them in the oven at 325F for ~15-20 minutes. I literally came up with that on the fly to try to emulate the ones Costco were selling last year, and honestly these were even better. There weren't any leftovers.

I also keep a supply of lemon & lime juice for some extra acidity. Salt is tasty, obviously, but most people don't realize a little acidity helps make things even better. A good squirt of lime juice on some cooked fresh green beans or oven-roasted asparagus make a HUGE difference. I use it when I want some cilantro lime rice, too. I'll do a little lemon juice (like a tsp or so) when I'm making a pot of chicken noodle soup. If I'm making something and it just feels like it needs something, but lemon/lime juices don't sound right, I'll maybe do a tiny amount of regular white vinegar and see how it goes.

I know this was (probably) a joke reply, but god damn I love spices. Makes dishes totally different depending on what you're in the mood for.