Typically one reload for whatever I'm carrying.
In my truck there is a P97 in a floor safe. There's often also an 870 in a locked case.
My truck door pockets are full of shotgun shells leftover from various hunts in the last year or so. I could hunt anything from doves to deer with whatever I find in there.
My truck console also tends to catch the spare mags and or speedstrips/speedloaders that I cast off in my daily travels.
My truck is well armed typically......
.