If you use antivenin wrong it can do you more damage than the bite. Rattlesnakes aren't like some African and Australian snakes- you do have time to get to medical attention, and they are rarely lethal even without treatment (although not fun). They also deliver "dry" bites (without venom) a significant percentage of the time, particularly older, larger snakes. All the snake is trying to do is chase you away, after all. He's got better uses for venom. The current recommendation is not to mess with tourniquets, cutting, and suction, but just keep pressure on it and keep it below heart level if possible, keep calm, and get to medical attention. If you get a live bite (envenomated) it's in your system almost immediately, and no amount of suction, tourniquet, or amputation is going to keep it out. I'd second the recommendations of much more experienced posters than me on this thread- get snake gaiters, know where your nearest hospital is (you should know this even if you're not in snake country- trust me), and don't worry about it.