Here are my recent bursts of creative outputs:
Giant mustache: This was for the Steampunk World's Fair, and I keep it around for any non-rainy or indoor occasion where it might prove useful. It's basically just a couple cut pieces of cardboard with furry fabric and lots of glue -- some hanger wire keeps it attached to my head, a hat hides the wire, and a little bit of bubble wrap helps to prevent the wire from creating permanent valleys in my scalp. If I can make it there, I could certainly use the stache for September 10th's Coney Island Beard and Moustache Competition.
Wearable boat: Two sets of double-layered cardboard rectangles glued together in brick formation and cut into boat shapes. I held them together with twine so that they bowed around me (the front and back were ~9" apart, but the middle sections were 12" apart, since that's about how wide I am). I also made a quickie spyglass out of different sizes of cardboard tubing. It all went well, but by the end of the day one of the sides developed a permabend.
Ball pit: This is ultimately for Playa del Fuego and the Geeky Kink Event. It's basically a framework of PVC piping and some plastic netting around and plastic balls inside. The basic design has approximately a 4'x4' footprint, and I so far have 1450 balls. This isn't even enough to halfway fill it. When I get back from the other side of the continent, I will have to get more. I beta tested the pit at my housewarming party, where we managed to fit seven people inside before it started losing structural integrity, and I was also given a few hundred balls as gifts for the ongoing project. At the GKE, about a thousand balls will be waiting to help the total. I'm figuring that once I hit 2000 balls total, I'll make sure to have extra PVC on hand (including additional vertical cross beams and more tees) to allow for a larger pit.
homemade slip'n'slide: This came to me suddenly a few days before my housewarming party. It was so easy that I'm surprised I've never seen it in practice. I got some plastic sheeting, put it on the ground, and sprayed it with water. Bam, instant fun! As an additional bonus, it makes for a serviceable tarp!
Bubble wrap flag: Castles in the Sky is a yearly parade (in previous years it held the much cooler "Kaleidoscope" name) in which people dress up in fancy colours and random things and going all around NYC with musical instruments, bubbles, hula hoops, and similar bits of funnery. It has fire shows and aerial silk performances and other interesting attractions. I had my bubble wrap shirt all prepped, but since people make flags for the event, I decided to temporarily grab some of my ball pit PVC, buy another roll of bubble wrap, and make a flag out of it. People liked it, and it doubled as entertainment at the afterparty when I laid it on the floor for people to stomp on between musical performances.