Sneaking contraband in to the Survivor beach would be pointlessly counterproductive. First of all, how do you intend on sneaking this gear in “under the prodcer’s noses” when your campsite is swarming with camera crews? Pulling a
Magfire out of an orifice before your tribe has actually been rewarded firemaking supplies will certainly see it confiscated and quite possibly get you kicked out of the game by the producers for a rules violation. Also, I can't help but think contestants are required to sign contracts agreeing specifically not to bring contraband, so you could also set yourself up for legal issues.
Secondly, in a game where your "tribe" members vote people off based on popularity and strategy, cheating is suicide...
Now, in spite of all that, if you really wanted to try to cheat, what would you need?
Water purification is really a non-issue. Tribes invariably have access to water sources, containers, and the opportunity to use profligate amounts of firewood with which to boil it. Fire making has never really been an issue after the first few days. The show was a little more cavalier in the past about food, but I’ve noticed that after they almost strarved the Survivor: Outback contestants to death, they’re much more generous, at least with starches (and, unfortunately, alcohol). Protein seems to be the thing missed most, which leads me to suspect that fishing gear would be the best bet to bring, so you can stay ahead of the curve until it finally shows up in a reward challenge. Since I don’t believe in cheating, though, were I to become a contestant I’d do what I could to research regarding the improvisation of fishing tackle from found objects rather than trying to sneak in tackle.
I love Survivor; it's one of my very favorite TV shows, but I don’t really watch it to pick up on survival skills, although there are some things to be learned, if only by those who don’t put much thought into the subject. “Don’t camp in dry creek beds” is a notable example. It pains me just the smallest little bit to see it derided for not being a wilderness survival skills course, since that’s not what it has ever aspired to be.