mixed bag

NOUN
9 LETTERS · STARTS WITH M

mixed bag is a valid 9-letter word worth 21 points in Scrabble and 24 points in Words with Friends.

SCRABBLE WORDS WITH FRIENDS
M3I1X8E1D2B3A1G2
3 + 1 + 8 + 1 + 2 + 0 + 3 + 1 + 2 =21 PTS
DOUBLE WORD → 42TRIPLE WORD → 63
MEANING

What does mixed bag mean?