All you need is a normal frisbee to play our course, However, your enjoyment and skill level will be significantly higher if you purchase a specialist golf disc. These discs are generally heavier than normal frisbees, allowing for significantly more distance and control. Here is a link to an online, Newcastle-based supplier.
Other Recommendations As well as a decent disc you will probably need footwear that you don't mind getting dirty. We say this because the recent weather has left some of the trails a bit muddy. You should also make sure you wear long sleeves and trousers. There are a few nettles and midges knocking about which can make it an unpleasant experience in shorts. If you have any midgy repellent that would definitely be recommended. Most of all though, you just need a good sense of adventure and you will have a great time!