Your all important Walker number, of course! But also its worth checking out the weather forecast the day before and making sure you're dressed for it. We've been lucky every time, wonderful sunshine at Kielder and very few midges but this is Northumberland and things change!
Personally, we would recommend sunscreen, midge repellant and a light waterproof plus if you're bringing a dog, your other doggie accoutrement including poo bags of course!
You will also need to either bring a reusable water bottle or buy a Walking for Wag bottle on the day or from our online shop in advance.