Question How to implement my power-up system

I'm creating a metroidvania-like game, and the main system is using different creatures that help the player beat enemies or access new zones.
I'm not very advanced in Unity but I know stuff.
What I'm trying to create is a character that follow the player all the time, and when pressing a button it does an action. The thing is, when you get more of these, I wanted to create a system where you can switch between them.
I still havent started doing scripts but I wanted to have this solved first. I think it could work like, a script that detects if the player has come into contact with the gameobject and obtained it, and then store it and make it so you chan change between the ones you have obtained and stored.
I honestly have no idea how to do this so any help i appreciated.