Notebooks would be a great item to be able to spawn, allowing for people to create pretty neat custom maps and challenges , it would also be cool if when you BEAT your challenge (got all the notebooks and got to a exit), they respawn, allowing for you to test it out, But what about exits? you may ask, Well what i would do is just use a elevator model, and then close it, either that or a baldi door,
Next on the list is The tape player and the phone, which would work like how you expect, simple,
Next is a character, Gotta Sweep, i think this would be pretty easy to add, just make them go around the map, push whatever characters they catch, and return to their spawn point
Finally, Id probably add a "Friendly" Baldi which would stop any aggressive baldis from spawning until you collect two notebooks