When I first got this pack I thought it was going to be too small for my needs. I was looking for something that could carry my clothes for post-work workouts, carry the essentials for day hikes, carry the essentials for geocaching, be small enough to use for trail running, and small enough to not be too much while cycling. This pack has, so far, provided me with all of these things. The ability of it to be small and large for whatever the purpose is exceptional. I can fit undergarments, three shirts, shorts, and warm-up pants inside the pack. I then attach a sweatshirt on the outside and stick my Nalgene in the provided pockets. For geocaching I am able to carry all the essentials I need, plus the water reservoir is perfect. The bite valve has an on off switch, and it delivers the water very nicely. This pack is awesome for many different activities. I highly recommend it!