Don't wear makeup if you don't want to. I was convinced that I needed makeup and an updo to look formal in pictures, and I don't recognize myself in many of the pictures- I wish I had worn my hair down and the simple makeup that I usually wear (mineral powder, mascara, lipstick or gloss).
I think it's important to be authentic as possible at the wedding. Any professional photographer should be able to capture what you look like without the tools of makeup, unless you're in extremes of lighting or using flashes in the dark.
If you're inclined towards sunscreen (as daytime weddingers should be!) I second the recommendation of -Neutrogena sunscreen spf 45 no oil. It's the best sunscreen I've found yet.