1
general::
What remains and need not be mentioned; and the like. For example, The display room is full of stereos, TV's, and what have you. Although first recorded in 1920, this expression uses an archaic form of putting a question (using have you instead of do you have) as a noun clause, and what in the sense of "anything that." The synonym who knows what is much older, dating from about 1700; for example, When we cleaned out the tool shed we found old grass seed, fertilizer, and who knows what other junk. Also see OR WHATEVER.
American Heritage Idioms