A lot depends on time of day, location, amount of people attending, etc...I usually wear church dress to anything where I want to look nice. I love dressing up and wearing heels and hose. I know, I'm goofy. But I wore hose and heels to classes in college. A lot of times at the beginning of the semester I was mistaken for the professor when I walked in. I think unless it's very casual, like at the beach or a picnic that a nice dress and semi high heeled shoes would be appropriate, maybe not spiked but more solid looking. If you are going bare legged then work on a tan, nothing is more noticable than pasty pale skin.
As for a gift, they tell you what they want on the gift registry. It amazed me when we got really odd gifts at our wedding that weren't even close to what we registered for. We ended up with many, many, unusable gifts. My husband was 37 and I was 33, had been married before, and was a sinlge parent. We both had homes we had to blend. We really wanted the things we listed because they were things we had picked out together. We did get some money and we used it for spending money on our honeymoon. Original things are often well thought out and special too so don't discount it just because mine didn't work out that way.