Rubber, apparently. You'd think that was a trick question, wouldn't you?
URB DIC Rubber Bands in the Pants: V. To wear physical birth control after it has been used once. many rappers do this so that they may have "quickies" in-between songs at shows.<br />
"I got the Rubber Bands that were in 50 Cents Pants, but they were crusty and dry so I had to take care in selling them on eBay." <br />
- Fred, in accounting. <br />
Doug: "Jake, wanna go to my mother's house for supper?" <br />
Jake: "Can't buddy, Ive got Rubber Bands in the Pants." <br />
Urban Dictionary--sadly many entries seem to be fact based
In the entire history of man- I assure you this was done