Clothing Wear casual clothes that you don't mind getting a few grass stains on. Athletic shoes or street hikers are appropriate foot wear. Leave the designer jeans and the Air Jordans at home. Sandals, cowboy boots, high heels, etc. If its been rainy you may get some mud on your shoes.
Long jeans are probably better than shorts.
Your never know where you might come across poison ivy, mosquitoes, ticks and assorted shin or knee scrapers. Other valuable commodities would include insect repellent, sun screen, a hat, and a water bottle. Restrooms will be available but they may be a short walk away, so keep that in mind. If the session overlaps a meal time, a sack lunch is a good idea. There are no Big Macs, pizza delivery people, or waiters.