I am apparently a glutton for this stuff because several years ago I gave my kids a big Halloween Party (so not even someone's birthday!) and called it the first annual Halloween party. So now every year we do this party. We all dress up. We make the yard a graveyard. I make cheese spread in the shape of mummies etc. - you get the idea. Design and make Halloween themed games and treats and so on.
Birthdays are often big events also. My favorite was the Beach Party in the winter.
I actually enjoy the planning. The costs can get crazy but we make a lot from scratch and I order from Oriental Trading co. At this point I have leftover unused items that I can reuse also.
