1) A WHITE SHIRT (if you're a shirt person) or a white blouse (if you're a blouse person). You can dress it up or dress it down. Wear it alone or as a layering piece under a jacket or sweater. It has long sleeves (with the option to roll up if a shirt) or 3/4 (bracelet) length. The shade of white is the one that most flatters you. For some that may be closer to ivory. It fits you perfectly.
2) BLACK PANTS in an all-season medium-weight wool or blend (yes you can wear wool in warm climates). They also fit perfectly and are of a current style. They are hemmed to the right length for the shoe/s you wear with them. There is nothing to stop your having multiple pairs of black pants from capris to palazzos, but you need one that is perfect without being a huge style statement on its own. Today I would say that is a flat-front, straight-leg style that falls comfortably from your hip.
3) A LITTLE JACKET has its own personality and doesn't "match" anything. For some it can be a tweed (think Chanel), for others a well-cut denim. You can pair it with separates to make an outfit. You can grab it for warmth as you run out the door.
4) One piece of REAL JEWELRY that you wear Every Day not just for Occasions— a string of pearls, a gold bangle, real diamond studs, your grandmother's cameo. When you put on real jewelry you immediately feel better dressed.
5) A PARTY DRESS— one dress (or outfit) that you can count on when an invitation arrives. It doesn't have to be black but can be a color that is season-less and looks great (teal flatters many). It's wardrobe security and will avoid panic if you do go shopping for that event and come home empty handed.
Bonus must have (if you wear them)— JEANS that fit. Simple dark denim in a current and flattering style. Jeans go in and out of style regularly so one pair will not last you a lifetime.
Five Things NOT to Have in Your Closet:
1) Anything you wore in high school or college, even if it still fits. Put it in a box. Label it. Store it away.
2) Any item of clothing that is really a costume— in other words, it isn't you. You bought it because you felt like Lady Gaga that day. Or your best friend. It was probably on sale.
3) Anything that itches, scratches, pulls, rides up, slips down.
4) Anything that is yellow but is meant to be white or that is gray but is meant to be black.
5) Anything that didn't fit then or doesn't fit now.