Being "Boo'd" is basically spreading Halloween cheer to your neighbors, family and friends. You take a little token (whatever you want that to be - you can make it as simple or as elaborate as you want) to your family, friend's and neighbor's homes. You put whatever it is you brought on their doorstep, knock on the door and RUN! You don't want to be caught because they aren't suppose to know who left the treats. If you know what May Day baskets are all about, then this is the same concept, just a different season and holiday!
You can find "Boo Kits" in stores sometimes, but they can be pricey. You can make your own at home for a fraction of the cost! I basically decorate a bag and then put Halloween candy or trinkets in the bag and then type up a note for the outside of the bag. Something like: