any hidden stuff in mario kart 64?

I recently went back to Mario Kart 64, and I’m having so much fun with it again.

Now I’m trying to complete everything and really “finish” the game, but I’m not sure if I’m missing anything. Are there secret unlocks, hidden modes, or tricks that aren’t obvious?

Is there more to do after beating all the cups?
What should I make sure I don’t skip?