Perhaps the most essential piece of portable equipment you can buy, the buddy lee speed rope can be carried literally anywhere, and can add a great deal of variety to outdoor, and, indeed, all workouts.

The most important move to master for CrossFit is the double-under or power jump. In the double-under, the rope simply passes under the feet twice for each jump. To perform the double under, one must first learn to jump fairly quickly. Maintain a neutral body position (upright), keep the feet together and turn the rope with the wrists, not the arms. At first you may want to try jump-jump-double-jump-jump-double. Another way to get your first one is to spin the rope as fast as you can from a dead stop and jump high: don't keep using this method, but you may want to do it to prove to yourself that it is possible to do.

Get the Aero Speed Rope, which I highly recommend, here.