In this scene,
Do we think that:
a) They don't have schoolbags for some reason (why???? that's a lot of books!! you cannot carry all of them comfortably!)
or
b) They're employing the age-old teenager stratagem of "well our next class is like five minutes that way and I'm not repacking my bag just to unpack it again when I get there. everyone load up"
or
c) Mysterious third option
Remember, this is 1959.
The first modern backpack was not invented until 1952, but they did not gain popularity because they were heavier. A lightweight nylon version was invented in 1967. But it didnβt really become popular to use as a school bag until the 1980s.