There's always a couple of fishing rods and all my tackle, a TW Sherrin and pump, a pro scrabble set and official scrabs dictionary, and at least a six pack of Melbourne Bitters in the boot of my duck.
Problem is I don't have a fridge.
Lucky for my summer Saab adventures, one of the Myth Busters blokes told Metafiler readers how to get their cans cold real quick.
About 20-25 minutes in a freezer. If you put it in a bucket of ice, that would halve that time. If you put water in that ice, it'd be cold (+- 5c) enough to drink in about 4-6 minutes, if you put salt in that water, you'd reduce the chill time to just over 2 minutes. Agitating the can in the water, rolling it around, reduces the chill time even more.
The fastest possible way is to grab a CO2 fire extinguisher and unload that sucker on the can.
Whatever you do, do NOT bury the can in sand, pour gasoline on the sand and set the sand on fire. That won't do anything.