If anyone wasn't aware, tennis balls cut in half make for great "cones" to use as practice in parking lots.
If you ever feel like setting up more advanced drills for yourself, they work great. They are...
Cheap
Light weight
Bright (easy to see)
Stable on the ground
Easy to make
Fit in saddlebags
Safe to run over on accident
Won't break easily
Just be sure to buy DDFM's Drill book and cones first... THEN, supplement with chopped tennis balls.