I think you left off the gift card to Pep Boys, Gryph.
My tank bag holds a second faceshield for night driving, food, water, maps, pencils, sunglasses, headlamp and batteries, a couple of carabiner locks, maps in all their quaintness, and any supplementary layers I may need to wear or shed for changing weather.
In the underseat box are a dial air pressure gauge and a pair of mechanic's gloves. Folded on top of the box is a small packtowel. That's it for there.
In the tail cowl I carry spare headlight lamp, tail light and brake light bulbs in small padded pouch, the air compressor, tire plugs, a tool roll with a set of take-down wrenches plus a combo screwdriver, spare fuses, golf tees for fuel line plugging, a valve stem wrench—just to help others, I hope—and a small bottle with some Go-Jo., along with a couple of rags and a pair of side case hinges. That's it for there.
The side cases are my bike's crashbars. They've taken a couple of titanic drops and what breaks are the hinges—almost as if by design. A spare set lays flat in the cowl or a side case, takes up little space and installs in a couple of minutes.
My cases hold clothes and food,. Raingear, a 45 year-old SVEA 123 stove, and its fuel bottle go into the tail case.
A tent. sleeping bag, sleeping pad, collection of ceramic owls, train timetables for India, Chile and Texas, a spice rack, a pair of crutches, a tourniquet signed by the catering staff of "Rescue Me", my reloading dies, cases and flatnose hardcast bullets for my 44 Rem. mag, my gunpowder dispenser, footbath basin, a pound of Epsom salts in a waterproof, bearproof container and other boring utensils go into a waterproof duffle strapped down on the seat in front of the tail case.
For all other contingencies I depend upon a lifetime's experience in:
1) the benefits of regular mechanical maintenance;
2) the bitter taste arising from the neglect thereof and—above all;
3) magical thinking.