What are some underrated features of your favorite packs?

Seconding the earbuds. They are especially useful in university I've found. Listen to them whilst studying and on the way to/from class on the long journey. You can cram in lots of studying and do basically nothing fun aside from listening to them if you want to, it's great. I'm wondering if you could get away with doing the same in GTW careers. Making non-fun things fun by using them.