The only time I shoot at a "range" is when I'm in AZ for the winter. Those trips are "planned" so I don't carry extra ammo in the car . . . 1 - we are careful about what we do leave it he car in case someone breaks in to it (whilel in a parking lot) and 2 - the car heats up pretty good if it's parked out int he sun.
If a person carries and is on the road a lot and sometimes has an unplanned trip to the range, I can see stashing a box in the car. Which I believe the OP is talking about.
If you're talking in regards to SD . . . as stated, why woul you need any beyond what you would normally carry in your CCW weapon and extra magazine (if you carry one)?
If a pair of '51 Navies were good enough for Billy Hickok, then a single Navy on my right hip is good enough for me . . . besides . . . I'm probably only half as good as he was anyways. Hiram's Rangers Badge #63