mixture vs grab bag

mixture and grab bag both are nouns.

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

As nouns, grab bag is a hyponym of mixture; that is, grab bag is a word with a more specific, narrower meaning than mixture:

mixture (noun)	grab bag (noun)
the act of mixing together	a container from which a person draws a wrapped item at random without knowing the contents
an event that combines things in a mixture	an assortment of miscellaneous items
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)