Well basically be sure to take your laptop with you and right after the wedding go eat yourself full and then vanish, find a network to connect and dive into the "Real World"
Really best advice, in that way you can't be bothered and you won't be bothering anyone...For sure;)
[color=#FFFFFF]I say again just have fun and be open minded. I've met quite cool people at weddings (mainly people invited from the "opposite" side of the wedding ring). If your sis has a short temper I think bringing an electronic device to entertain yourself on her big day will definitely piss her off
I also find it mildly amusing how everyone including myself turned into a wedding survival artist within 4 pages