Dustin added, "As for the running bit, sure it can be done without an essentials kit but it's not really recommended. All it takes is a bug unexpectedly flying into your face while running down loose scree to make you lose focus. One misplaced step and you've got a bum ankle miles from help with a cold storm moving in. "
Exactly my point. It's not some sort of survivalist paranoia, but more conceding that poop happens and it doesn't take much to improve your chances for surviving a simple mess like a fall. Again, it seems that all the stories involve one small indecent compounded by a string of others: he fell, and then this happened and then he did this and then that happened and it took SAR two days to find him, near death.
My first thought for a runner was something like an 8 liter hydration/day pack with a good bounce-free suspension. Even a small lumbar pack could hold enough to keep you alive.
I wonder how many runners tell someone where they are going?
"A day hike in the PNW might require a more robust basic 10 essentials kit than a day hike in the late spring in southern CA where I wouldn't have to worry much about rain, cold or bugs."
The weather today at roughly 3000' in the Central Cascades (Snoqualmie Pass) at 1:48 PM is 43F with 60% chance of precipitation and an overnight low of 38F (overcast, of course) and 89% humidity. Directly above the pass at 5400' the temp is 35F. The trails still have lots of snow and getting off track could leave you with some nasty post-holing. The open trails are more like small streams and things are muddy and slippery. Bugs will be more of a problem in a few weeks.
We lost a couple hikers last year from sliding off snow-packed trails and down cliffs. Just a partial fall would leave you in bad shape and certain to get wet and cold. Bad place to spend a night without a little gear.
Keep in mind that the trails are commonly on the vertical side in the PNW. From sea level in downtown Seattle, you are looking at 7000'+ peaks in the Olympics, not to mention a 14,410' volcano in the back yard (54 miles), with a couple more 10,000'+ volcanoes for good measure (Baker and Glacier). Mount Rainier has more prominence than K2! You go from the suburbs a half hour drive from the city center straight into designated wilderness areas. I think that closeness fools people, like they are going for a walk in an underdeveloped park. It is just 50 miles up I-90 to the Pacific Crest Trail at Snoqualmie Pass where I mentioned the weather conditions above. I can literally go from the Space Needle and be walking the PCT in an hour.
So this is my playground: beautiful and full of hiking opportunities, but it is steep, wet, cold, dark, and heavily forested. It is wonderful to experience, but not very forgiving if you screw up.