I assume that you can get under the front hood of the car....
Being VERY CAREFUL, I would use jumper cables to put 12 volts from another good battery to ground and the big starter cable on the car. This should power up the car to allow you to open the trunk

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My Truck.. 2007 DODGE, 5.9 Cummins, 6spd stick, 4X4. My car..1977 240D, OTHER WHEELS...1955 VW Oval window bug, European Delivery (Holland) with a 1700cc, 2 barrel, Porsche drum brakes. 1939 WILLYS Pick-up. 1967 Triumph 200cc Tiger Cub. 1976 Honda 550F 4cyl Motor Cycle.