Way to go Mike!! Glad you are finally going to do a gathering. I know you are kinda shy but don't be - you will love every minute of camping with these great folks.
One thing you might want to do is make sure you have a good supply of wood. You will probably have a group campfire going pretty steady, depending on the temps during the day.
Start making a list or ask for someone to give you ideas for your list. You've camped many times so you pretty much know what to bring anyway. But for gatherings, a lot of us will have a Saturday night pot luck dinner. If there is no electric, I'll bet there will be a lot of black iron cooking going on.
You will be surprised at how much fun you will have. And not to worry, if you forget something, someone will have it. Don't forget your camera!! We want to see lots of pictures! Relax and just have a good time buddy!