Not sure about you but here is what I keep in the trunk:
Bug Out Bag (clothes, food, water, cash, etc.)
Emergency Roadside Kit (commercial one from Canadian Tire)
Tow Rope, Booster Cables, Battery Pack (12V booster), Air Pump, spare light bulbs (headlight, taillight, turn signal), fuses, tools, flashlight, candles, matches
Oil, Washer Fluid, Water (4 gallons in old washer fluid containers), hydraulic fluid,
Old track suit (for changing tires in), blanket, windshield cover (heat shade)
Probably some other stuff that slips my mind but that is the bulk of it. Remember you don't know where you will be when TSHTF.
PS I belong to CAA (like AAA in the states) but don't count on them being around after TSHTF so want to be prepared.