And, if you take mics and a PA sytem, be sure to take wind socks for the mics!

I just played an outdoor wedding last week and even though we were in a tent, the wind came up and it was damned near impossible to hear your voice or instrument in the monitors for the roar of the wind.

It didn't actually sound so bad for the audience, but trying to sing with that racket in the monitors was hell. I actually blew the words to a song because I coudn't concentrate.