According to JN, here are the locations for the Halloween bags:
(you need an account to see links)
(you need an account to see links)
(you need an account to see links)
(you need an account to see links)
(you need an account to see links)
You'll receive these bags, respectively:
There's two new stamps you can receive from the IGS:TG or MI Kitchen bag:
You can also receive the Neopets Halloween theme, permanently, by refreshing on the site at 12:59 PM NST. Thanks to @(you need an account to see links) for that.