Paper treat sacks
Anything else on the clearance aisle!
Wait until things are at least 75% off. (Trust me...there will still be options after you wait out the 50% sales.) Check out places like your local drug stores in addition to Target and Walmart. You can also find great deals at craft stores like Michaels and A.C.Moore.
Treat bags are sure to be a hit with everyone who rings your door bell-and you're sure to be the most popular house on your street.