That's an interesting way to look at it as not how long your planning to be out but how long you might end up being out.
I ran into a woman once that told me her husband makes her take pretty much an entire pack load of gear when she day hikes just in case. That's one way to say how much I love you.
It's called prudence. I was heading up to San Bernardino Peak last summer, when the lightning and thunder got to be too much for me...emphasis on me. I people past me on the way back while was descending with no rain gear or 39 gallon trash bags.
I go out in the winter and regularly see people climbing high angle slopes with Microspikes and trekking poles.
You calculate risk and throw in a bit of what happens if I screw up when setting up a pack. I've seen a climbing accident, been involved in an accident where only one first aid kit in 12 was good enough to care for the injured person and screwed the pooch a few times myself. This all adds up to a pack that is sufficient to spend an extra night out and care for most medical emergencies.
