I use an REI Flash 45 as my pack for both day hikes and overnighters in the White Mountains. It is bigger than it needs to be for a simple day hike, but it works well. It is plenty light itself, and since it is the same pack I'll be using with a heavier load, might as well get comfortable with it. I also tend to over pack for day hikes, but I don't really feel like getting caught out while peakbagging solo. I'd be pissed if I froze to death because I rolled my ankle and didn't have a simple emergency shelter system with me or something.