Fair warning: Even if you've told Great Aunt Mildred that you're not having kids, she'll probably start with the "so when are you going to make some babies?" business during the reception... some time between dinner and cake.
We were pretty open about our intentions with friends and family before the wedding, but some people seem convinced that now that we're were married, it's high time to bust our chops about how "selfish" we are for not wanting kids, or about how "oh, you'll change your mind", or something equally insulting and/or patronizing.
My suggestion: Poke around Google for "childfree bingo" and keep a copy with you. It'll help pass the time.