Camping and backpacking
When someone says daypack, one of the first backpacks I think about is the Maxpedition Falcon II Pygmy. Its lightweight, has plenty of room for year, and has 2 places for a 32 ounce water bottle.
Inside of the pack I carry:
Hammock
Rain Poncho
Poncho liner
Food
First Aid kit
GPS
2 Compasses...