Use Saran Wrap, along with painter's masking tape, to cover portions of a wall you don't want painted, leaving them one color while you coat the rest of the wall with a second shade. This technique allows you to mask larger portions of the wall than you can with tape alone and/or create unusual shapes of masked areas, like twisted ribbons of plastic pressed to the wall. Coat the entire outside edge of the plastic wrap with tape to ensure a watertight seal.
Use Saran Wrap as a rough stencil to apply paint patterns through holes in the plastic. Lay out a sheet of plastic on a clean carpet, and poke holes in it using something like a nail or pencil. Masking tape the plastic to the wall, and apply the paint; it will ooze through the holes and drip and smear on the other side of the plastic. Make many holes, or just a few, but space them out evenly on the plastic wrap for best results. You can also layer with this technique, applying another layer of color over the first.
Use a wadded-up ball of Saran Wrap like a painting sponge to make interesting patterns of paint on the wall. Use just one size of ball, or make different sizes of balls for different parts of the same project. Experiment also with how tightly or loosely you wad up the plastic; tighter balls have more compact, dense lines. For best results, arrange your wads of plastic so that they have lots of wrinkles and parts of the edge of the cut wrap.
Make a single-use "brush" by rolling up some Saran Wrap into a tightly-wound roll and cutting along the end of the roll with scissors. Seal the "handle" portion with tightly-wrapped tape, and use the brush to apply paint in a quick, sloppy manner, pressing the brush against the wall rather than stroking with it to give you imprints of the edges of each plastic bristle.