I would start with an LBD, knee length, either elbow-sleeve length or sleeveless. Add:
1. Microfishnets
2. Strappy high heels (metallic?)
3. A clutch (better for juggling drink and handshakes) in a bright pop of color
4. A statement necklace - something artsy
5. Bring a cheeky jacket in case you get chilly... leather, denim, BF jacket, all could work.
You could also be more daring and pick a dress in a color other than black. There will probably be a sea of women in LBDs, so why not stand out?
I would not dress up as formal as you would for a wedding. You want to hit a note a touch more casual than that, and more fun.