How do I bind down my boobs?

For the best results, you'd want to do like the transsexuals do and buy a gizmo called a chest binder. These are mostly sold on the internet and are possibly more expensive than you'd want. But you can get a pretty good effect by using a sports bra with a smaller cup size or a torso-minimizing camisole. Even a snug t-shirt under your costume can make the shape of your breasts less obvious. All of these things should be available at Target or any other decent-sized woman's clothing store, but you'll get a better selection if you go to a fancy department store like Nordstrom.

I'd actually avoid the ace bandage trick. It's popular but it's tricky to put on right, it can restrict your breathing, and the edges of the bandages can dig into and cut your skin. If you opt for that, just be aware of these issues and don't leave the bandages on for too long.

Wear a tight sports bra, or even better-get a WIDE ACE bandage and have someone wrap your chest in it. You can get ACE bandages at Walmart, Target or the Pharmacy, in the First Aid section. Good luck!