I keep a fan belt, hoses and an ignition tune-up kit on board all the time; nestled in the center of the spare tire along with a towel (to lay on). For longer trips (overnight), I might add an electric fuel pump with some hose & clamps plus a loaded distributor (with new points etc, cap & wires). But since I've never actually needed them, they are probably just wasted space.
Lug wrench, jack, jack handle and a pry bar for the hub caps are also in the spare tire well all the time. On board tool kit has an assortment of Whitworth wrenches and sockets, SAE wrenches and sockets, SU tool kit plus the usual screwdrivers, pliers, etc. Burnishing tool for points and VR contacts, set of feeler gauges and spark plug gauge. Tie wraps, 'baling' wire, assortment of nuts and bolts. Tool for the headlight rings. DMM and clip leads in a separate box, along with the registration papers, quart of oil, small bottle of DOT 5 brake fluid.
Driver's door has several flashlights (I really like the LED "head" lights), disposable gloves and of course the "budget lock" key.
And of course I always carry my "Tinker" model Swiss army knife, which has Philips and flat screwdriver blades as well an an awl, can opener, etc.