It depends a lot on what you're looking to improve. If it's your general health and physical ability, which will of course return in spades in your kung fu training in addition to more energy and the ability to take your shirt off at the beach, then I'd suggest doing some sort of cardio exercise 2-3 days a week to start. Aside from the usual running, swimming, jumping rope, etc, you can incorporate practicing your forms at a "fighting speed" (just don't get sloppy) and do some shadow boxing. Also, make sure you stretch EVERY DAY for at least 10 minutes (30 if you can spare it) - its the only way to increase and keep your flexibility up and increase your range of motion. Oh, and if you do strength training, focus on your core and abdominal muscles.
If you're looking for something more kung fu related, I would say the best thing to do as a Jow Ga student is to invest in either a heavy bag or some focus mits or thai pads, or all of the above. Practicing your techniques against a target is best, especially a moving one with the mits/pads if you have someone that can work out with you (they don't even have to know kung fu - just how to hold pads!). This will help you to develop more power, precision, speed, and control in your techniques.
I'd could go on all day, but I'll stop here for you to mull over it abit!