Excellent choice of venue. Just so you're fully prepared here's a list of things I like to take with me to skirmish:
Good boots with proper ankle support - You will be playing on multiple terrain types so your boots need to be good for everything. This time of year it's pretty swampy in places.
Change of clothes - At a bare minimum a clean change of socks or two. I like to take light clothes for the drive home. Tracksuit bottoms and a normal cotton shirt + jacket or something
Sling - Even if you are renting its always good to have your own sling... The weapons get heave after a while!
Money - Run out of ammo? No problem, just go buy more. Cant do it without money. They take card at the grange as well though
Food and water - VERY important. You can buy food there but its always good to prepare a sandwich and lots of water to keep you hydrated. Especially on the hotter days when people drop out due to dehydration. I started in the summer and on my first game 3 or 4 other new people left early because of this
Those are just the basics. I bring more stuff myself but thats just me. I havent seen anything on the website for a shoot on that day, but if it pops up i might go along I prefer to play at their Honiley site though. Maybe I will see you around! Enjoy your shoot!