Truck guns I've known and used:
'58 Remington, various pistol-gripped 12 ga, Ruby .38 spl, Ruger Super Blackhawk, M1 Carbine folder, Ruger Security Six .357, Norinco 213, various SMLEs, Rossi .32 long, various Win 94s, RG 66, and many others.
Figure one long gun, one short gun, and often one hide-out GTH gun.