A crayon in the communal Primary Three colouring box which we unanimously held to be such an enchanting, perfect, GREEN shade of green that we would fight tooth and nail for it every single morning.
Competition was fierce, and once in your possession, you would be subject to aggressive attention and intense paranoia - if you let your guard down for a moment, it would be stolen away.
If you went to the toilet, you took it with you, and did so visibly - otherwise your desk would have 29 children crawling over it when you got back.
The One Crayon was finally destroyed by Donna McGhee, who inexplicably vomited all over it.