Useful post on Reddit today: http://www.reddit.com/r/Guildwars2/comments/11zzng/earn_5_personalized_trick_or_treat_bags_for_the/

These should be per-character, so you can probably change characters to get even more of them…and the first few being in Lion’s Arch and early Queensdale, characters levels 2-80 are able to go hunting.

Happy Hunting!

Edit: the nodes in Lion’s Arch have been removed in today’s update.