You guys have come through for me in the past two years.
So, round three.
Sunglasses, sandals, volley ball. Voila, you’re a nudist!*
*You might want to wear a flesh-toned bodystocking and a strategically placed fanny bag too. 
Get four or five small, stuffed dogs. Attach them to you by their mouths. You’re a fence jumper.
Name tag that does not have your name on it.
Take a black magic marker to a tee-shirt - 404: Costume not found
Cut arm and head holes in a big cardboard box. Anytime someone asks who you are, fall to the floor. You’re Dropbox.
Still wearing the box, complain childishly about things. You’re Boxed Whine.
Or slap a sign on the box that say’s property of Pandora and go as Pandora’s Box.
Finally, all else fails, put the box to one side and quietly cogitate. You’re Thinking Outside the Box!
Cardboard harpoon, a stuffed whale, and a nametag that reads, “Hello! Call me: Ishmael”.
Not REAL simple but not too difficult either. Materials: Blue or black jump suit, silver duct tape, silver spray paint, 4’x4’ (+/-) piece of cardboard, hot glue.
Fashion the cardboard into a zipper pull. You know, the sort of triangle shaped thingy with the tab. This is a 3D replica that is big enough to fit over your head. It should have sides but no top (lets heat escape). The sides need inverted U-shaped cut outs for your shoulders. The whole thing should be maybe 20" high and 12"-14" deep. Probably 12" at the narrowest spreading out to 16"-18" at the widest. Hot glue works great for this. A helper would help.
Once fashioned, cut out a rectangular eye hole. Just beneath the eye hole goes the pull tab attachment. The tab is about 4" wide by a foot long. Don’t forget the hole at the bottom of the tab. The tab needs to be glued to the head piece in a manner similar to an actual zipper pull. Cut out a mouth hole on the head piece that will be hidden by the tab but still allow you to speak (or more importantly, drink) by lifting the tab. Spray paint everything silver (or gold or black). Use matching color duct tape to make the teeth which you will tape to the front of the jumpsuit. Include the legs if desired. I used tape to make the letters “JACK” and put them on my back. Taa daa…Jack the Zipper. I did this on the 100th (?) anniversary of Jack the Ripper’s rein of terror and his story was on the news quite a bit at the time. I won the contest. Alternatively, you could call the costume “The Human Fly”.
Be sure to sketch out the shapes before cutting. I’ve actually used this get-up twice. It took a while to make the first time but after getting the learning curve down I was able to do it in about an hour.
Assuming you’re male, you can always airbrush some shadows and stick some fake hair on the bodystocking to make it less obvious. And make sure you carry a cell phone and some Coppertone in that fanny bag, along with other accoutrements. (Family Feud once did a whole segment on what a nudist might carry in one.)
Or an “I LOVE WASHINGTON D.C.” t-shirt and you’re a White House fence jumper.
Handcuffs and antennae and you’re an illegal alien.
Some say that by using a motorcycle helmet painted white, a dark visor, and white motorcycling jacket and pants you can go as a “tame racing driver” or one of his cousins…