Fits:
Extra layer of clothing
Extra socks
Water bottle
Bag lunch
Sunblock
Insect Repellant
Cellphone
MP3 Player

Fits:
Change of clothes
Warm layer of clothing
Towel
Water bottles
Hydration Reservoir
Food and snacks for the trail
Headlamp
Sunblock
Insect Repellant
Camera
Cellphone
MP3 Player

Fits:
Change of clothes
Jacket
Ice axe and shovel
Trekking poles
Water purifier
Stove, fuel and matches
Water bottles
Hydration Reservoir
Food and snacks
Headlamp
Sunblock
Insect Repellant
Camera
Cellphone
MP3 Player