I think the must-have lists are helpful, but I've adapted them and made them my own:
1. Instead of crisp white button down, my must-have is a silk button down -- gives the same look, but much more comfy and easier to wear.
2. Instead of a turtleneck, my must-have is a cowl neck, which is more flattering for my short neck. I now have so many cowl necks -- sweaters, knit tops, jersey dresses -- it's not funny. In fact, I filled my "must-have" striped long sleeve top requirement with a cowl neck rather than a crew neck.
3. I do have and rely on the LBD but as I get older my ideal must-have would be an LND - navy is more flattering than black, but just as versatile.
4. Instead of a khaki trench, my must-have is a cream trench; much more flattering for my coloring.
5. Instead of 4" pumps, my must-have is 2-3/4" pumps.
6. Instead of white cotton tee, for a long time, my translation was a white blouse in silk or crepe or other dressier fabric. Then I finally found some white cotton tees that fit my fussy standards.
... on and on it goes...
Whenever I have added one of the "must-have's," as long as I've been VERY careful and picky and adapted to my figure, I have found the item to be just as versatile as these lists make them out to be.
That said, I do find I reach more often for certain must-have's. I reach for flattering black pants much more often than flattering jeans. I rarely wear my pencil skirts because just a few pounds weight gain can throw off the fit. And this whole thread is only reinforcing for me where I really need to update/replenish my wardrobe -- which is another thread entirely. I've been making a list.