I have a small BOB I've used a few times. It's actually a child's backpack; black nylon, several compartments. It did around 20,000 miles on the back of my Suzuki in its role as a tailbag. It had the usual stuff - earplugs, first aid kit, wet wipes, bag of quarters, Leatherman tool, glasses/face shield cleaning supplies, an aluminum plate on a lanyard I could slide under the kickstand and loop over the clutch lever when on soft surfaces, etc.
From time to time the bag had its contents rearranged a bit and went along on road trips in cars, and once to the hospital with me when I had kidney stones.
Last Thanksgiving I got a midnight call from my Dad's housekeeper; "come now." Dad was 83 and in declining health. I tossed my 7-inch Android tablet in, a spiral notebook, and a couple of paperback books. And then spent most of the next two weeks sitting in a chair by Dad's bed as he fought his way out of a massive stroke. Two weeks ago he had the first of a new series of strokes. In his last lucid moments he wanted to go home, so when the doctor said there was nothing they could do - they had discovered several aneurysms, blood clots, and lung cancer, all inoperable - they sent him home via a hospice outfit. He lasted two days, and passed quietly in his sleep this afternoon.
Four and a half weeks wedged into a hospital chair is close enough to SHTF for me. The properly-equipped bag helped a lot. I spent a long time in a chair near Dad's bed, as the hours turned into days, then weeks.