I can think of a couple crazy things you can do:
1) Name the day after me
2) Give me the key to the city
3) Void all my parking tickets
Pretty much that would make my day. I mean check it: how many people get a day named after them? Can you imagine, let's celebrate
But I mean what do you give your kids when you are the mayor. You got all your political friends at the wedding, so its got to be something good. You get a certificate commemorating the day signed by no other but, YOU. It is kind of corny but very cool at the same time. It is definitely something you don't see all the time and just adds another memory that the guests go home with.
I'd rather still have the key to the bank though.