Toolkit? Depends entirely on how self sufficient you need to be.
On-pavement near civilization: Fix flat tires, tighten anything that vibrates loose, adjust mirrors, basic chain lube. I carry an electric air pump, a small manual bicycle pump (in case the electric fails), 2 tire pressure gauges, a tire patch kit, a tire plug kit, Snap-jack, tire irons, bead-breaker (motion pro brand), wrenches, vice grips, screw drivers, rags, small chain lube, paper towels, disposable gloves, a piece of cardboard (to protect rear rim during chain lube then toss in trash). Duck-tape, regular & needle nose pliers, small socket wrench and sockets, hex wrenches, flashlight. A tire valve tool and spare cores is recommend by many though I've never had or needed them.
More remote and/or zombie apocalypse: Adjustable wrench and a larger socket wrench to remove rear wheel. Two chain master links and 2 links of chain, chain breaker tool, small voltmeter, spare clutch cable. Possibly a tire tube in case of major tire damage, though you will have to remove the existing valve and deal with a different size stem, so this is a pretty extreme case item. Repair or spare items for your camping equipment (fire starting, taping ripped tent or sleeping bag, spare batteries and flashlights, phone charging somehow, etc).
If you are going long long distances: Oil and spare filters.