Pick 'n' mix
A range of sweets, chocolates, ice-creams etc., from which a selection can be made.
The 'n' abbreviation might lead you to think that this is an American phrase. If so, you would be right. It originated there in the 1950s, as a slogan to advertise sweets - or should that be candy?
The first evidence that I can find of it in print is in this advert for F. W. Woolworth, from The Cedar Rapids Gazette, 13th August 1958.
Since around the 1970s, the use of phrase widened from food items for sale has been used more generally to denote anything that is made up from a selection of various items; for example, from The Times, July 1974, in an advert for a television programme:
Pick 'N Mix: Ronald Fletcher with recollections.