Collectables, or, in American English, collectibles, are items of human manufacture considered worth keeping. People collect all types of things, from valuable antiques to seashells to cereal boxes. There is no hard-and-fast rule about the hobby of collecting, however, although people may collect both naturally-occuring and manufactured items, only items of human manufacture are considered collectables.
Collecting should be distinguished from hoarding, usually considered an unhealthy pastime. Hoarders collect items compulsively and store them in higgledly-piggledly fashion, often just piling them in their living spaces.
Collectors, on the other hand, ensure that their collections are clean and sanitary; they are stored neatly and often displayed in shelves or cases intended for that purpose. Collectors also organise their articles; details of a small collection may be kept 'in someone's head', but large collections are generally catalogued. Furthermore, collectors acquire their items systematically.
Even collections composed of items of apparently no intrinsic value can end up having a monetary value, due to the size, nature, interest or scarcity of the collection: baseball cards and cardboard cereal boxes are examples.