Right now I have a large backpack for travel (~40L), a smaller backpack for everyday (12-20L), and a small packing cube for use in the airplane (5L).
I looked at other backpacks (listed under "some examples" below), but I realized that I do not really need another one.
The only things I would improve upon are the aesthetics of them.
The everyday backpack is torn up. I could get a new one in a similar style or slightly larger size.
For the small packing cube, I could get something a little more stylish, for use when traveling.