I currently use 2 AirTags. One of them is on my wallet (it has a slot for an AirTag) and the other is on my house keys keychain. The wallet one has helped massively a few times when I accidentally left it in the car (if I don’t find it where I expect it to be, it means it is either somewhere close or somewhere safe). Been thinking of getting one for the car keys, but haven’t found a nice keychain for it yet.