I never thought of this as a cool idea. Someone at worked commented on how clever it was. I call it the Poor Man's Space Bag.

Materials:

A trash bag
A twist tie

Lay the trash bag out flat on a soft surface with the opening facing the edge. A bed or sofa cushion works best.

Put neatly folded clothes into the bag.

Fold the extra trash bag edges underneath.

Sit on the bag.

Flatten out the remainder of the bag underneath you to push the air out.

Starting as close to the clothes as possible, begin twisting the extra bag about 10 - 15 times.

Secure with a twist tie.

It'll stay vacuum sealed for about 24 hours. Saves me room in my backpack on my commutes.

Hope it helps someone!

-Adam