Steven Coffman mentions a need for a 12v fridge  for under $100.
I have found the Thermo-electric Coleman cooler , (http://www.avidoutdoors.com/co40quthco.html) to be very useful. It’s a shade over $100 list, add the 110v power supply and you go to $140, but Walmart usually has ’em with the power supply for under $100.
I’ve found though a few years of use, though that this thing really works best when you help it along.
First, I’ve found that the fridge running all the time will kill any car battery in about an hour. It’s simply not practical to keep ’em running all the time on the vehicle battery.
Secondly, even asuming no power consumption issues, the thing will only keep stuff at 40 degrees below the temp of the outside air, without help. (Or, if you wire it backwards, it’ll get 100degrees warmer than outside air. (Great for hauling Thanksgiving goodies to Grandma’s house… and yes, it’s designed to do that.)
So, by the numbers, if it gets to be 80 outside the fridge, 40 degees is the best you’re gonna do INside it. If it’s 90-110 outside, hang it up, son, you’re done, and so is the stuff in your fridge.
What I’ve done to counter this situation in my van, is to wire it to a 12v feed that is only on when the van’s running. This requires a change of attitude about what is the primary coolant.; Your attituude should be that the primary cooling isn’t the powered part, but rather, the gallon jugs of ice. To keep the thing cold during those times when the van is powered off I keep one or two gallon jugs of ice. (How much ice I start with depends on how hot it is for the week, and what kinda space I need inside the box) With this system, we’re able to do quite well for several days; it keeps everything quite cold. The longer we run hte truck per day, the longer the things stays cold.
Most of our trips are camping type trips, or just straight road trips… and they run under four days, so this works just fine. I suppose some of these ideas are from the pop-up-camper’s mindset; make use out of every ounce of space and power you can, for multiple purposes. See what you think.
I keep one- gallon milk jugs of ice… two in the van fridge and two in the freezer at home. In this fashion, I’ve found myself able to get about 4 days out of the van fridge, before I need to change out the ice, even in high summer. That’s far longer than just a regular cooler. When the first pair of ice jugs is melted, I simply switch them out with the ones in the basement freezer. I keep at least a couple six packs of drinks and or a gallon of kool-aid on hand at all times durning the summer, even when not over the road. It’s nice, coming hom from work with a cool lemonaide in hand. There’s always one waiting for me.
Additionally, I’ve found that there’s an advantage to this system I’d not planned for; We’re able to bring water from home, without wasting space. You see, my wife has a problem, sometimes, with water from other sources. So, the water I freeze is filtered water from home. A couple of days from refill/refreeze point, we’ll have water to drink.
Sometimes, I even make a gallon of kool-aid, or iced tea, or something, and freeze THAT, as one of the gallons. We’re experimenting with freeing the Juice pouches you get at the store, just now. The kids like them, and they minimize spillage inside the van, of course… plus they are great for tight packing in the fridge. But we’re using some of them as ice bags, too… First time worked OK. Keep ’em near the top and they’ll melt in a day or two. My concern is will they burst… but so far we’ve been OK. Keep some unfrozen for immidiate consumption, but freeze some, and pack ’em right, and you’ll extend the life of your ice bottles, is the idea… while adding no space requirements inside the box.
Sometimes, I’ll also partially freeze bottles of storebought lemonade and such, too. And of course if you’re camping, freezing the burger, chicken, dogs, and so on… even bread and rolls you’re packing for the trip, will also help extend the life of your bottled ice, and will give you a little peace of mind of the stuff being fresh when you need it. I’m even playng at cooking up a couple lbs of bacon, and breaking it into bits and freezing in a couple smaller containers for use in eggs and such. Saves space and weight over uncooked bacon, and in frozen form helps keep the ice going, and keeps longer, too.
I do have a 110v supply for the thing, which I will use in Camp mode; the van is wired for 110VAC… which is connected the moment we make camp… so the fridge is basicly running 24/7 which will keep the thing cold well over a month before the ice melts. That may not be practical for your car, but I’m just sayin’.
Hope these ideas help.