Some GREAT tips at the following website and I will share my own with you, as well.
I always keep my pets locked up in a room so there's no chance of them getting out. If your pets get anxious with the doorbell, please, talk to your vet about a sedative. OR, sit outside with your candy so there is no need to ring the bell.
Also, keep an eye on the candles-cats love to get close to them and their whiskers can get singed.
CHOCOLATE is toxic for pets. Xylitol (in sugarless gum) is also toxic. If you think your pet has gotten into your Halloween stash, CONTACT YOUR VET--IMMEDIATELY and/or ASPCA Animal Poison Control Center at (888) 426-4435
Also, if it's after hours and your vet is not open or available, there is a fabulous Emergency Vet Clinic in your area...Have their number stored in your favorites on your phone.