Leftover soda bottles from your most recent summer barbeque? Put them to use in a game of backyard lawn bowling -- you'll need 10 2-liter bottles, and the empties only, please.
To turn soda bottles into pins, first give them a wash and dry, and then fill each bottle with a little gravel or sand -- the amount isn't scientific; you're just trying to weigh them down to reduce the odds they'll blow over (or away) in the wind before you can knock them down with the ball. If you want fancier pins, remove the labels from each bottle and paint them with plastic-friendly paint -- try white with two red stripes for a classic pin style, paint them the colors of a rainbow (plus white, brown, and black to bring your list of colors to 10) or take advantage of the clear plastic bottles and fill them with decorative items.
Mow yourself a bowling 'lane', set up the pins, grab yourself a ball (about the size of a bowling ball is perfect, although backyard bowling balls can be -- and probably should be -- much lighter) and hope for a strike.