I don't count, but would guess at between 30-40? They have pillowcase sized sack 'stockings' and they contain a mixture of things they asked for on their letters, aswell as other things I get because I know they will like them.
Haven't bought anything yet (do mine in December) but for example, dd1 (12) will probably have... a cd, lush bar, bath bombs and lip scrubs, shower jelly, perfume, makeup, novelty socks, whittards hot chocolate tub, sharpies or other pens, Smiggle scented rubbers, charm for bracelet, cinema voucher, obligatory satsuma and chocolate coins, named Nutella jar, soft penguin, books.... and whatever else.
Doing their stockings are the best thing about Christmas shopping!