My super quick geek tip is also green: turn your old mouse pads into coasters with five minutes, a pair of scissors, and a pencil.
Just take your mouse pad and mark pencil lines so you know where to cut. Use a ruler or a straight edge for neat edges. Then, simply cut along your lines, and ta-da! Instant coasters ready for the party. You can get creative too with different shape cutouts or adding designs to each coaster.