I dont have a dedicated car gun, but do own a G19 with a TLR1, purchased NIB specifically to be a beater. The TLR1 recently replaced an M3. When I bought it, the Insight/Streamlight M3 was the light to buy if you couldn't afford or justify the cost of a Surefire. I couldn't justify the cost for a beater.
Beater rifle was a converted 7.62 Saiga with an LED G2 mounted with a cheap scope ring. Gone now, hard times, had to pay rent...
Beater shotgun was my only shotgun, a mossberg 590 with a surefire fore end.
They fill the truck/trunk gun role well. The pistol goes with me quite a bit. Long arms, not so much.
I normally took the AK to the lake cabin, it was compact due to the folding stock. When camping (real camping), I normally took the shotgun, but the AK would sleep in the truck unless I was with another trusted adult.
If I were shopping today, specifically for truck guns, I would probably pick up a cheap used Mossberg 500 without a vent rib, and cut the bbl down to 18.5" (with a pipe cutter), and swap my old 590 stock onto it (synthetic, stippled, chopped).
The rifle would probably be a cheap Fudd milsurp.
I miss the days of being able to sink hundreds into a beater... I like ARs, but would prefer .30 cal for four legged critters. If I had the cash I would consider a .300 blackout kit from Model 1 Sales since it doesn't look like the AR47 will ever be.