The earliest Halloween costume I can remember having is a little clown suit with pom-poms on the front made out of green yarn. My grandma made it for me, and it's pretty cute, although I am terrified of clowns now, so I don't think I'll be passing that one on to any future children we may have. Other costumes include Madonna (maybe 3rd grade?), a hobo (complete with a coffee ground beard), and the Phantom of the Opera.
In 9th grade, we hosted an exchange student from St. Petersburg, Russia who happened to arrive on October 30th. At that point, I was only in my 3rd year studying Russian, and my language skills were limited to introducing myself and explaining how my fictional Russian friend, Tatiana, and I purchased sweaters and books on our recent trip to GUM. Our exchange student, Ekaterina, had never trick or treated before and I did my best to explain the process to her as I handed her a mask and an empty pillow case. What I explained to her in Russian (her English was no better than my Russian) probably translated back into English as, "We get candy. We are walking to many houses and say please give me some candy and then say thank-you."
My junior year at Boston College, I wore a full suit Winnie-the-Pooh costume that I bought at the Disney Store. I purchased it then reasoning that it would come in handy when I had to walk my own children around the neighborhood on Halloween in the freezing cold. My roommates and I went to an off-campus party that year, and after several beers and jello shots in a packed house, I realized the Pooh costume was like wearing a fuzzy sauna. I passed out in the middle of the party to enthusiastic shouts of "Pooh's down!" (or so I'm told.)
I am driving to CT today in order to attend a baby shower early tomorrow afternoon with my mom, but hopefully I'll be back in time to help pass out some candy. My Pooh costume is in CT, and I'll break it out for the first time since college to answer the door, but will be extra careful to stay hydrated this time.