You realize you have completed all exercises you need to, your muscles feel taxed, but you want to do more. What do you do? I'm looking for any helpful answers but kind of hoping to get some muscle group specific suggestions.

An obvious one is do some cardio to cut fat. I'll give an example though; on back/bicep day I will sometimes throw in some hand and forearm exercises. Reverse wrist curl. Grip exercises with a barbell behind my back. ETC. Yes a proper back day with heavy deadlifts etc will tax the biceps, forearms back etc. But I can visually see my wrist get bigger doing reverse wrist curls and thats no shit. I can see my hand get just a little bigger by targeting it. I'm not looking for "essential" exercises; just stuff you can throw in on those days when you really are enjoying the gym.