Here is the item again:
Syed finally decided to clean out his disorganized book
bag,
old U.S. 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 U.S. 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.