The Jansport Syncline 38 is a great basic small pack that I purchased to use as a "loaner" pack for friends I take backpacking. At 2350 ci many consider it just a daypack. However, as a lightweight backpacker, I find that it is plenty big for the gear I pack for my novice friends to carry - ultralight down sleeping bag, tent fly and poles, water, food and extra clothing.
Personally, I could use the Syncline 38 as a 3-4 day pack. It is lightweight and one of the smaller packs to include a framesheet and stay to distribute the load to the hips. Unlike many backpacks, the Syncline 38 is equipped with the storage organization options I think are important - water bottle pockets and enough other pockets for storing clothing, rain gear, food, flashlights, etc.
I compared a lot of similar sized daypacks (North Face Big Shot, Marmot Talus, Lowe Alpine Powder Peak, North Face Terra 40, Kelty Redwing 2400 & 2650) to find a small pack with a lot of features at a good value to use as a loaner pack for my friends. The Jansport Syncline 38 is perfect!