My $0.02:
I'd go a second fridge, as the others have said. It gives you heaps of options and flexability. We have a 47L ARB, and I'm seriously tempted to pick up one of these:
http://www.getawaeco.com.au/default.asp?id=416&catId=6...to run as a freezer. I find we don't need a whole lot more fridge space, but having a small freezer would be really handy for long self-sufficient trips. So long as you're not into it all the time, running a small fridge as a freezer won't take a huge amount of extra power. Certainly it would use significantly less than a 3-way fridge on 12v.
We used to use our ARB fridge for food, and the father-in-law would take his 3-way fridge for drinks. We wouldn't run it on 12v at all - cooled down at home on 240v, left closed up while in the car, set up on gas at camp. Even thought it was only small, because it would cool the drinks quickly most of the cans stayed hot in the carton and as you grabbed one from the fridge you'd re-stock. Worked well, but eventually he got sick of mucking around with the gas/having the pilot blow out and warm beers/having the gas smell at night, etc.
The other option is to do as a mate of mine does. He has a single 3-way fridge, and two iceboxes. The fridge is set to -10 and used just as a freezer - all it does is freeze 2L milkcartons full of water. He takes these out, and puts them in the iceboxes. All the food/fish in one icebox, all the drinks in another. As soon as the milkcarton iceblocks melt, they get swapped back into the freezer and the cold ones go into the eskies. Voila - everything stays cold, the eskies keep getting "new" ice, cheap to buy and it's very economical on gas. Plus if you're ever in trouble, you have heaps of spare fresh water in the milkcartons. Doesn't work for me because it's such a big setup to put together. Perfect for him - he heads up the cape/gulf for 4-5 weeks at a time to fish and makes camp in one spot. I like to be able to move more often, and having the fridge in the car means my drinks/lunch is always with me.
tl;dr - if you're lazy like me a second small fridge is the height of luxury, so long as you can afford the cost of entry.
Good luck!
Matto