Snake bite kits are a waste of money on not just the AT but any trail in North America. They often do more harm than good.
FWIW, the Wildernes Medicine Institute suggests splinting the bitten extremity, not elevating it, do not do any unnecessary exertion, treat for shock (get in your sleeping bag) and then evacuating. They also stress to not use any harmful and unproven treatments. Reading between the lines, that suggests to me snakebite kits.
On the AT, are you no more than five miles from a road (and rarely, if that) with plenty of people coming by. Worse case? Treat yourself, put yourself in a position where you can see people coming and going and you should get help in a very reasonable window of time.
Rather than a snakebit kit, it is easier, lighter and less expensive to be aware of the surroundings. The PA rocks have some rattlers, but they are easily avoided. (A case to NOT wear an iPod while hiking.
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