When thinking about the outfit for this, you don't want the spotlight to be entirely on you, but you do want it to stop long enough to notice that you're there. A simple sheath dress or strapless dress would be perfect for an event like this; classic shapes that work for almost any evening affair. For country club gatherings, I tend to think more of a "garden party" event. I would recommend leaning towards the conservative side and bringing a cardigan or pashmina or cover your shoulders. I like to steal the show with the added extras, such as jewelry and other accessories. An awesome necklace, bracelet, or earrings would add to the look of understated elegance.
Even a day-to-night sheath dress in a fun color would make a great backdrop to great accessories!