Holloween event question
Dunno about different cities, but IMO its not worth it to travel to different cities, just wait for another game day. You have to give the npc's different sweets in order to get items/costumes. For example, If you have some garlic crackers, and 3 kinds of cookies, the max number of times you can try for an item/costume in a game day is 4, one for each type of sweet you have. You can trade more, but all it will say is "Thank You" and you won't get anything.
I've gotten 2-3 items in the same game day in the same city this week. I do not know if you can get more then 3 seeing as how it is rare to get that many period but I do know that there is no limit to the number of times you can get costumes. My characters were using 7-8 different types of sweets when trading and on average out of 16 trades or so I'd get 14-15 costumes and 1-2 items. Of course this is over 2 game days and I did have rare good runs where a character got 2-3 in one game day but that was really rare.