C, V, X, B, and Insert to open the menu, and to check what effects you have, and equip them.
Z, Enter, and the spacebar are to accept details.
1 is to use an effects ability, 2 is to cancel it, and 3 is to drop the ability (only in the main area with the doors, and should be done once you've gotten all 24 items).
And 9 is to wake up, where you can save (by moving towards the desk and clicking enter), and play the minigame.
It depends on which weird character it is. Some of them do nothing if you try to interact with them, unless you use the Cat, Knife, or Stoplight effects on them (Cat makes them move in your direction, Knife kills them, and Stoplight makes them stop in their tracks, for most of them, at least). However, some of them do in fact carry effects. Most of the ones that do stand out a bit more than the ones that don't.
Here is a strategy guide, by the way. Feel free to use it if you want, but the maker suggests not using it to figure out where the items are unless you really need to, which I agree with; a great part of the game is just looking around and seeing what goes on in the player character's head. However, if you're going for the items in a certain order, I suggest the bike first, which is pretty easy to get. XD