Ace Bandage method:
I use 6"wide NON-STICKY ACE brand (brand is important! ACE is much more resilient!) bandages, with the clip closure, not the velcro kind. (Walgreens usually carries 'em.) Wrap around, but not too tight so that your ribs hurt, adjust what you have under them up and out to the sides. If you are "bigger" than I (most women seem to be, including my 12-year-old daughter), you may need two of them. If that's not enough, ACE bandages are not your method of choice.
Advantages: Easy to adjust, or take off and redo in the ladies' room.
Drawbacks: Bandage shows with a low-cut shirt.
Bandage tends to wiggle down after a while, and needs some pulling up. If you wrap down the ribs as well, this is minimized (but DON'T wrap too tight on the ribs - you WILL be in major PAIN. )
It works well enough, but I thought I could breathe better with the tape, and it constrained the muscles less. Like I said, though, I may get s*** from the SO if I try the tape again.
In any case, by the end of one day at Y-con, I just ditched the bandage altogether and went around with nothing on under that tank top - it felt soooooo good to be free....
I've tried the "control-top panty-hose used as a "tank top" method". (The legs & crotch are cut out to make the armholes and neck hole.) I'm NOT impressed.
a) It didn't flatten ME out enough. (!!!) Maybe enough for a loose thick shirt high-necked shirt - but *I* need REALLY flat.
b) The "shoulder straps" really dug into my shoulders very painfully from the moment I put it on. NOT acceptable.
c) You have a seam up the front of your body.
Faye Valentine: Attached should be a pic of my family cosplaying at AX03.
Karasu: The armor is made out of Celluclay, over a base made from pieces of plastic collander and cardboard. It's not as nice as I wanted it to be, because it needed about 5 more days of spackle & sanding that I did not have... Oh well *plans to re-work it*