On short notice, I'd use the age rule - a 3 year old can have 3 pieces of treat-size candy, a 5 year old can have 5 pieces (if anyone gets a full size 8 ounce candy bar, that doesn't count!). Followed by serious tooth-brushing.
Do separate out the toys - in our neighborhood, half of us don't even give candy because we have a diabetic kid plus those with allergies, and for everyone else it just gets thrown away anyhow. So let the kids play with the stickers and Halloween puzzles/pencils, wear the spider rings, and toot the kazoos. Do some "triage" on the candy, choosing what to eat now, what to save for rationing out over the week, what to give away, etc. The food pantries will take the leftovers (though they'd prefer nutritious food), and we have a few area dentists who collect the leftovers and send them to deployed troops (who presumably can monitor their own candy intake!). If you can find anyone in your town who does this, it wouldn't hurt to have the kids think of those who don't have what they have.