Toddler medicines

My son is 3 and I’m just curious, what types of over the counter medicines do you keep on hand in your household for your toddler? I’ve realized I don’t have many medicines for him on hand so when he ends up needing something most of the time we don’t have anything to help him and have to go buy something. I want to be better at keeping medicines on hand for when he needs them. What do you use/recommend/can’t go without? TIA!