I've found the PB Adventure Vest to be optimal for day long self-supported expeditions. I've used it on multiple 50-60 mile runs in the mountains throughout the summer as well as some less technical climbs. The capacity is ample for carrying plenty of food and water as well as extra layers and emergency overnight gear. However, the sizing does run small when it's loaded, so order a size up.
This review was written in the old system and had content requirements that are different than reviews written today.