Stamp booklets were designed as an easy method of buying a number of stamps in one go, often from a machine so that they could be purchased outside post office opening hours, usually housed in thin card covers to protect them so that they could be carried in a wallet or handbag. In the early days a small premium for the convenience might be charged. Naturally, booklets in the early days were rarely preserved, so very old intact booklets are extremely rare; those that survive might contain just a few stamps and are often not in good condition. Later, booklets were sometimes issued with commemorative covers, often to mark an occasion that was not quite important enough for a stamp issue. Often the covers bear a printed date or serial number; many collectors choose to try to obtain all the variants.