grab bag vs mixture

grab bag and mixture both are nouns.

Word	Noun	Adjective	Verb	Adverb
grab bag	Yes	No	No	No
mixture	Yes	No	No	No

As nouns, mixture is a hypernym of grab bag; that is, mixture is a word with a broader meaning than grab bag:

grab bag (noun)	mixture (noun)
a container from which a person draws a wrapped item at random without knowing the contents	the act of mixing together
an assortment of miscellaneous items	an event that combines things in a mixture
	any foodstuff made by combining different ingredients
	a collection containing a variety of sorts of things
	(chemistry) a substance consisting of two or more substances mixed together (not in fixed proportions and not with chemical bonding)