Here are some ideas of what you could do:
Earings, if you love your earrings this would definatly be hard. BUT you can wear them on Sundays!!
Candy, this is what i'm doing and it is HARD.
Meat, one of my friends is a "vegetarian for 40 days"
TV, I don't watch alot of TV but some do.
Perfume, my mom's friend did this one
Wear nothing but sandles, for me this would be a treat but for those who live were it snows..
Painting Your Nails
Wear only skirts, or if you like this, wear only pants
Thats all I can think of right now. If you have any other ideas please comment!!