Eh, that's too bad. Mildew is pretty tenacious stuff. And some damage may be irreversible—mildew corrodes fabric and can weaken it considerably.
The first thing to do is make sure the mildew is dead. Brush the gear with a stiff brush to get off all the mildew that you can. Then spread the gear out in the sun someplace, bringing it back in at night if need be to keep dew off. The key is to get it as dry as possible. Plus, sunlight kills mildew.
Next, make up a cleaning formula of about a cup of lemon juice with two or three tablespoons of salt. Rub that into the mildewed areas. A solution made from two tablespoons of bleach and a quart of warm water can also do the trick, although of course that also can change the fabric color.
Anyway, scrub the mildew stains with your weapon of choice. Then rinse with water. Then, in the case of clothing, launder as you normally would. You can spray on a clothing stain remover before doing so, if you wish. In the case of the gear, fill a tub with warm, soapy water, and scrub the stuff thoroughly. Then rinse it and dry it, dry it, dry it.
Prevention is the best cure for mildew. Make sure stuff is stored where it can get air, and where things are as dry as possible. I know that's a challenge in the humid south. Perhaps you go to Home Depot and buy one of those gadgets that hold drying crystals, then place that in the closet where the outdoor stuff is stored.