For party favours, how bout pipe-cleaner spiders? You could attach them to safety pins to turn them into brooches/lapel pins.
Do you have large gourds in Costa Rica? You could make Jack-o-Gourds
Small, yes, but whaddya do when there's no pumpkins?
I like your balloon game idea! I remember, as a child, at the fall fair playing a game like that. There were playing cards behind each balloon which determined your prize. But candy or something in each balloon is awesome, too
I did some Googling and found some cute games. There's pumpkin bowling, where 2-litre pop bottles are the pins (with rocks in them to keep them steady) and you roll a small pumpkin as the bowling ball, but an acorn squash or other round gourd would also work. Also, pin the nose on the Jack-o-Lantern, which would be hilarious if everyone is half in the bag by the time you guys get to it. Lastly, eyeball bounce! You draw on a pingpong ball to look like an eyeball, and the goal is to bounce the ball into some container.
I've adored the idea of a photo booth for special events ever since I saw photos of a DIY wedding that had one. You just provide a prepared space with a digital camera on a tripod, a whole bunch of wierd and silly props and let people be crazy
You could have some picture frames, body parts, masks, a noose, a magic wand, a crown, funny glasses, mustache-on-a-stick (have a couple different mustaches), and whatever other silly things you can think of
Hope you all have fun!