I was flailing around on the forum trying to figure out what to wear to my friend's wedding in Las Vegas next weekend, so you can tell I don't have this done and dusted. I thought that I had a few pieces that would be fairly versatile but they were mostly evening wear, and for the cooler months as well - what Miss Manners would call cocktail wear.
What I do have right now:
a black wool pencil skirt with sequins, bought last winter on mega-sale and not yet worn
silver strappy sandals, ditto
a black ponte LBD, a little snug right now
a black woven tuxedo-inspired jacket which is quite dated in silhouette
black velvet drapey pants (good for Christmas/holiday parties with a sparkly sweater)
then I've got a few dresses and tops in my everyday wardrobe which could cross over depending on the event and time of year.
The problem is that I don't really need cocktail wear, I need a day dress or two (not black or white) that would work for weddings, christenings, 'informal'* parties, that sort of thing, some semi-casual stuff with a sense of bling for holiday parties, and then an appropriate outfit or two for a funeral, just in case.
*I say informal because that's what the etiquette mavens would call it, but it's the dressiest level I have ever needed to be in my entire life, excluding my own wedding and maybe prom. I've never been invited to a gala (I'd make a remark about meeting the Queen, but then Diana did!).