First here is a portal gun.
This spectacular, one-of-a-kind homemade Portal gun is for sale in this year's Child's Play charity auction to raise money to provide games and toys to sick children. The maker, Harrison Krix, has also documented the build.
Next is a portal shirt
Notorious hacker Benjamin Heckendorn -- aka Ben Heck -- has created a “see-through” Portal t-shirt that is perfect for freaking out kids at Halloween.
The t-shirt appears to show a hole through the wearer’s torso which reveals the scenery behind them, in homage to Valve Corporation’s puzzle platformer Portal. To create the effect, Heck cut a portal-shaped hole in the front of a t-shirt and positioned an LCD display behind the hole. On the back of the t-shirt was a CCD camera.
Whatever the camera captures behind the wearer of the t-shirt is displayed on the screen at the front, thus giving the impression of a gaping hole in the person’s torso. Unfortunately it doesn't work the other way -- there's no screen on the back. Though, that might make it a little heavy.
Heckendorn documented the making-of the t-shirt in his internet TV show The Ben Heck Show