A combination of "what do you/what are you/what have you" or "whatcha" with "Y'all" to form a compound word used to ask what a group of peoplethink, want, or do.
What'chall want from the store?
What'chall think of this?
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).