Carry On Zip-top Smaller Than A Quart What's Quart-size, Clear Plastic, Zip-top Bag For? Must All Of My Carry-on Luggage Be Put In It?

What's quart-size, clear plastic, zip-top bag for? must all of my carry-on luggage be put in it? - carry on zip-top smaller than a quart

I travel to Germany and I have a school bag of things with a few clothes and some medicines. And I have a small bag with some important documents. Can I use the bag for these two to fly with me ????? I do not want all the baggage.
What is the fourth in size, clear plastic, zip-top bag? If my luggage arrive?