This Knight’s satchel from Think Geek might be exactly what you need.
I don’t think it stops there though. As shown in the image; I think this bag makes for a great book solution. Got a bag set aside just to bring your books, dice and notepad to the gaming session? Help contribute to the atmosphere by using this bag.
Lastly, as a curveball suggestion, what if you’re an Ingress player? You’ll have a battery pack solution already? Right? Why not have a bag for it that’ll get both factions talking?