Back to school shopping: what’s actually worth spending more on

Q: Last September I bought the cheapest backpack I could find for my son because things were tight, and by December the strap had torn and the zipper would not close all the way. I ended up buying a second one partway through the year, so I probably spent more than if I had just bought a better one the first time. Back-to-school shopping is starting again already and I want to be smarter this time, but I still can’t afford too much extra. How do I figure out what is worth spending more on