I keep a spare set of casual clothes and a pair of old boots in the trunk about all the time. In the winter am old ski coat with a zip in fleece liner and some gloves.
as for the bag
it is pretty small and weighs less than my brief case if I am carrying a lot of work around. It is sort of like a courier bag only shorter, which is kinda dumb. I am just going to get a courier bag.
the small size is pretty much out of ready sight though
if I tighten the strap is is under the edge of my fleece
I know there is a lot of shit hanging off the bag, and I don't like the bag, but it is what I had around.
the radio goes in a pocket, the flashlight goes in a pocket, the red light (an LED bike light) stays on the bag and flashes like a bike light to keep cars from running over me and the watch goes on my wrist
Just like they teach you in the Navy, Davey Jones wants your stuff so tie it down. IF it hangs off the bag the lanyards are looped through a little carabiner type thing
front right side pocket
mini mag wid LED thingy, Zippo with a leakproof bottle of fluid, carmex, zippo, clippers, spare folding knife, bic, compass, ball compass pinned to bag, clip on LED flashlight, the red flashing light and a safety whistle
Top right pocket
leatherman wave, a special purpose key and a pen
flap pocket has the proper knife and another bic
power bars, clif bars, thumb drive with personal data, a couple of those stacker 5 hour energy things and a little means of coping from Mr. Walker
Big middle pocket, spare batteries for elec stuff, sunscreen (the skin grafts burn badly and they burn quickly), another bic, rolaids, zip ties, super glue, a few packs of hot hands, a buff, a fleece hunting hat, a buff, toothbrush with some loose OTC meds, another flashlight, a box of 50 rounds, army style poncho and a space blanket
well, seems sort of obvious I guess
Top pocket has the GPS in it
side pocket has a water bottle with a filter in it. Initial fill will come from some bottles in the car. Filter is for filling it on the fly until I get home. A 20 (it will be longer if I am taking surface roads, maybe 25-30 miles) could be a two walk so filtering river water may be needed.
truth be told the chances of needing this shit is next to zero, but I have been carrying around some version of it for over 20 years now. Carry a lot more shit when I had a truck, especially when I lived out west.