A laptop is indispensable so far as I'm concerned. Nothing beats having your own personal entertainment centre that you don't have to fight with anyone else over. Be prepared to have it get damaged by exposure to sand however- if I were to go again, I'd buy a cheap used one that I wasn't worried about breaking. Before you leave, you should load the laptop up with as much entertainment material as it will hold: games, music, movies, etc. Be aware that "adult" materials are considered inappropriate. Ensure that you bring enough gitch, socks, etc to stay dry in the summer, and enough cold weather gear to stay warm in the winter (yes, it's cold there in January). If you go to Mirage, you won't have to worry about cold, but don't forget that you might get sent to one of the other camps for a task or two, and you'll need appropriate gear.
I took a laptop and the stuff on the kitlist, and I was fine. It sure isn't like North America, but you don't necessarily need to bring the kitchen sink: a surprisingly wide variety of consumer goods can be bought over there for very low prices (though the quality is often suspect as mentioned in other posts). I can't think of anything that I could feasibly have brought with me that would have completely alleviated the biggest problem I had, which was boredom. The camps are very well developed these days and you can't complain at all about the facilities they have there, but all the same, 6 months of day-in, day-out routine will start to get to you eventually. My advice is to get there, wait about 2 weeks to figure out what your routine is like, and then decide on an appropriately time-intensive hobby to help you stay sane. There are no shortage of recreational activities available in Mirage, and even in the other locations you will likely have enough access to the internet to allow you to take an online course or some other such thing.