I usually have a box or two at least for whatever I may have with me, which includes a rifle at all times, and the spare loads often end up staying in the truck, unless its something I rarely have along. Not really planning for an alien invasion or screaming hoards of Canadians coming across the border (not YET anyway!), but just like having some spares with me. I also usually have a sleeping bag, and other camp gear in there, so staying out a few days wouldn't be a real problem if I wanted to. Biggest thing I'm concerned about other than choosing to stay out in the hills, is if a quake hit and I was in town or in the hills, the bridges could be out, and I'd like to be comfortable until I could get home.
"Far better it is to dare mighty things, to win glorious triumphs even though checkered by failure, than to rank with those poor spirits who neither enjoy nor suffer much because they live in the gray twilight that knows neither victory nor defeat." -Theodore Roosevelt-