For timing and a good plyometric workout, try jumping rope. Bongo bards are fun and are used by many national ski teams for coordination drills. Excellent cross training can be done through inline skating, tumbling classes, trail running, rock climbing and trampoline training. Strength training helps athleticism as well as helps prevent injury. Flexibility refers to the range of motion at a joint or joints and strength will help control those movements.
Most avid skiers like to work on their quad muscles and forget about the opposing hamstring muscles.
Work the opposing muscles and spend extra time on the trunk this season. An excellent resistant drill is to attach a rubber sport cord around your waist, then have a partner hold one end while you run. Your partner should provide enough resistance to keep you at bay. Try this while running sideways. This is the true test of your lateral movement agility.