If you're in the South, a nice long chain of kudzu makes a really great crown of ivy. The leaves are just big enough that it looks kinda funny :) And it grows in plentiful supply- enough to make crowns for everyone! Just knot them together in the back and use hairpins to keep them on.

seriously?
 

Haha, wow, kudzu? Really?

Considering how fast that stuff grows, I'd be afraid it would still be growing in my hair :p

I'm a fan of the halter-toga. Take the ends, and hold the sheet across your back, cross the ends over your chest so that it is wrapped and tie the ends behind your neck. Voila, support, coverage, and security.