A backpack such as this one can be very useful for a number of things. The grey colour looks quite neat.
From Amazon
Osprey Men's Duro 1.5 Backpack, Dark Charcoal Grey, L
Trekkinn
Osprey Duro Hydration Vest 1.5l Black L
Sigma Sports
Osprey Duro 1.5 Hydration Pack - Dark Charcoal Grey