When I was a kid, my mom and I used to go to the store weeks before Halloween and pick up several bags of candy to pass out to tricker-treaters. Those days, they didn't start displaying the Halloween stuff until early to mid October yet we still managed to pick up 2-3 bags of some sort of chocolate-y delight well before the 31st. Without fail, we would have eaten all of it by the time the actual holiday rolled around and would go out the day of Halloween and buy more to give to the costumed neighborhood children.
I'm not sure if I was a whiny kid and breaking my mother down or if she perhaps liked having an excuse to have some "naughty foods" in the house but either way, every year we ate all of the supposed Halloween candy ourselves. It often seemed like we used the excuses of "let's buy it now so we don't have to worry about it later" or "well, we're at the store so might as well". If you are one of those people who already has bags of candy in the house under the guise that you might not "go to a store before Halloween", I'm onto you : )
I'm not saying this from a place of judgment but instead of a place of trying to help you stay the course of your health goals (which housing a giant bag of mini Snickers or eating so many Mike&Ikes that your tongue turns colors is not contributing to your goals). Don't keep that kind of temptation in the house. Heck-it's been years since I've eaten what I would call "conventional candy" and you bet your a$$ it would be hard for me to keep away from it if it were in my home!
Do yourself (and your willpower) a favor and wait until Halloween Day to purchase your candy. There won't be a shortage-you'll have plenty to choose from. Or maybe hand out something other than candy (I know, everyone will hate you). When your kids come home with their loot, I suggest letting them keep a set number of pieces and donating the rest to our troops overseas. Maybe have your kids write a nice note to the soldiers too. So then Halloween can be fun and everyone can have some mainstream candy but no one gets to crazy.