If you want to do something extra, try filling out all 600+ enemy listings in the game.
There's a few enemies that are rare spawns and some can only be found at very specific locations that would otherwise remain unvisited.
Do this in tandem with completing the sidequests, there's one sidequest involving blackjack that has some weird way to unlock it instead of the list having it unlock naturally, that's the only sidequest you need to check if the NPC is up to start it.
The whole world in the game is worth exploring.