techntrek seems right on with his estimates, but I do have a couple things to add to each category:
Battery: although the stock configuration can get you through a long weekend, adding a solar panel can get you topped off each day if you stick to normal usage (efficient lights, water pump, light furnace use). Switching to LED lights can help a lot also.
Propane: we've found the fridge to be extremely efficient, but we camp in cooler conditions so that might help. We're running on our first tank of propane and I think it's about half full still. We use the furnace sparingly, so that might be part of the reason why the propane lasts so long. We have a small backup tank under the dinette bench (I believe it's a 4.5lb) for when the main tank finally runs out, but at this rate we could probably run for weeks on just the backup tank.
Water: once you get used to conserving water you can usually get about 3 days of normal usage on a full tank, BUT since the waste tanks are proportionally larger than the fresh tank, you can just fill it again. We bring a 2 gallon tank with us and use it to transport water from the nearest spigot to the rpod. It's a good workout, but you can extend you trip a day or two without much trouble.
Waste tanks: we've never once filled up the black tank (without intentionally filling it for flushing), and the same goes for the grey. I've seen several people transfer grey water to a "blue" tank and then dump it in a designated area (usually by the bathrooms). I've never needed to do it myself, but it's the same principle as with filling the fresh tank, but in reverse.
So... with all that in mind I think you could extend your dry camping capabilities to around 5-6 days with a couple tweaks and some good habits.