Essential is correct.
I love having bags to keep things organized, whether it’s a work (nurses MUST be organized!), while traveling (various electronic stuff…charging cables, extra external battery, reading lamp, etc etc), or just running errands (don’t want to lug around your whole purse? Toss your cell, cards, cash, chapstick, a protein energy bar), you’re set up and you have something light that you know will carry everything, and done beautifully.