Here is the sentence again:
Syed finally decided to clean out his disorganized book
bag, old US Government handouts, math notes
from Intermediate Algebra, leaky ballpoint pens, and a smashed banana littered
the inside.
Syed finally decided to clean out his disorganized book bag is a main clause. Old US Government handouts ... littered the inside is a second main clause. To connect these with just a comma is to create a comma splice, a major sentence error.
To fix the problem, you could put a period after bag and capitalize the O for old.