My commute was 20 miles, one way, and I drove a Jeep. Which in good conditions was a single days hike.
Which may not happen, it may be the worst of conditions. The New Madrid went off with an 8+ mag. quake, bridges collapsed, roads buckled, building collapsed across roads etc. Even though it's only 20 miles it would take more than a day, because the conditions could be very bad. There is not a single route to my home where I don't cross a bridge.
If on the other hand racial tensions went nuclear, I could drive way out of my way and avoid the communities where I suspect shooting would take place. Could still drive home but it would take way longer.
So my plan was to prep for 3 days which should take into consideration almost any disaster starting at my work 20. My biggest concern was protection against the elements, which I would use a military poncho as a poncho, and a lean to. Water, so I also had in my Jeep a military web belt, or tactical belt with 2 canteens, a big Bowie type knife, and a hatchet. Both of which would be used more for fire and clearing a path than defense, but if the need arose... And in the bag a life straw for clean water.
For food I had 2 items. 1) Energy bars, and 2) Bullion cubes. It's only supposed to be 3 days, so don't need much, but to walk for 3 days you do need energy. The bullion cubes was more to warm the inards, and give you a good feeling to sip something warm, from a fire.
A small first aid kit. Several knives, like a Swiss Army, pocket knife etc. Several items to start fires, a compass, and a 2d map, and a field towel, and an extra box of bullets.
And a hand gun, with fully loaded mags. Which wasn't so much for personal protection against an individual, which it could be used for, but out in the wild for 3 days, dogs, hogs, coyotes, 'coons, snakes etc.... There is nothing but country between the job and here.
The compass, map, clearing equipment was just in case I ended up going cross country, instead of following the road, which would be my first choice.
Now how big of a back pack would I need? I choose one with a sternum strap to keep it pretty much in place while I climbed creek banks, or was doing some swinging to clear a path. And had a pad for my lower back. Believe it, or not those really nice padded shoulder straps can feel like they are cutting into you after about 3-6 hours. Especially if you have never "hardened up" the skin over your shoulders, by back packing before, or your lower back.
It made the pack a bit larger than I needed, but empty space doesn't weight much.
Hope that helps with some ideas.
ETA: I wore steel toe shoes to work and back but kept hiking ultra dry shoes in the Jeep, Summer clothes for me no biggie, but winter clothes I kept a set of winter clothes extra thick jacket etc. in the Jeep in the winter.
