Thanks for all the great replies.

What kind of backpack? I need something that doesn't move around when I am going 40km/h.

I found this one online: MOMENTUM 22 - Osprey Packs Official Site

This one, https://www.amazon.com/Columbia-Cres.../dp/B004ZCJXY8, as ptempel pointed out is $250 dollars. Isn't that a lot of money? Does it have an extra strap around the waist to keep it steady?