I've lasted 23 days before. And I was in South India in July/Aug with temperatures of 28 degrees Celsius on average.
I think I lasted because I didn't have internet access and didn't buy any pornographic magazines. Another tactic to use is sitting on your hands for 10 mins if you get the urge, or put an ice pack on your trousers near your nether regions.
I have a theory - if you're used to fapping away predominantly to high-quality, long-length pornographic videos then without these your imagination will be rubbish and you will just not feel the urge. But after about 4 weeks you might come across a magazine/CD in your house with an image of a scantily clothed woman on it and the temptation will arise (even though you're used to videos and not static pictures).
One thing I wonder about though - is how long girls can go without flicking their respective beanie-babies?