I'm pretty sure this is why Angie encourages people to define their own essentials; it's so easy to get led astray by those "Every Woman Must Own" lists, or just by the amazing outfits other fabbers put together. Like others, I have very few of these items in my closet, although I can imagine finding "my" version of most of them if I felt like hunting.
1. I don't own denim shirts, but do have two printed chambray shirts. They do not have chest pockets, and they are quite tailored in fit. If they were sloppy, long, boxy, or had big pockets on the chest, they would not get worn (ask me how I know...).
2. I didn't have a denim jacket, or a desire for one, until last summer. I added a white one for the exact scenario you describe: a structured casual summer topper for jersey and knit dresses. Like Suz, I wore it until about the end of September and won't take it out until spring. It took a couple months of try-ons to settle on the Kut version; everything else I tried was too boxy, too stiff, too costume-y.
3. Never owned a trench coat. Not weather-proof enough for the kind of rain we get in the northeast, so they've always seemed a little frivolous to me. I do have "city rain coat" on my long-term wish list, but it probably won't be a classic belted trench. More like a waxed cotton Barbour coat or something, and definitely black or navy or olive, not beige or taupe.
4. I've tried a lot of white shirts and kept none of them, even though technically many of them fit. I like my shirts to be able to stand alone, and a solid white shirt just feels like too large a swath of white on me. I would have to treat it as a layering piece, like Deborah does, but that does limit its supposed "versatility" IMO. I do have "blue oxford" on my list for this spring/summer. Due to an influx of printed pants, I finally have a need for some solid-coloured shirts, but I don't think crisp white is the right direction.
5. Bootcut jeans. I retired my last pair last year. Vintage Red Engine -- I wore them into the ground. Really great denim, and cut just perfectly for me -- length, rise, everything. They were a unicorn and I miss them, but they didn't leave a gaping hole in my wardrobe. I came of age during the flare/bootcut resurgence of the late 90s/early 00s, so I had a stink-eye for any sort of tapered pants for the longest time. I have one pair of flared pants now, mainly because they are fully lined wool trousers in a plaid that I really love. I would like to find a new pair of sailor pants, which would be a full-length flare or wide-leg, but it's not a silhouette I'll go out of my way for. I have proportionately large calves, so jeans were always an easy fit for me back in the heyday of bootcuts, and it has gotten harder now that companies are designing legs that are so skinny and SO tapered.
6. Hah, I see you've added booties/shoeties to the list! This one is hard for me too. I find that the wrong height for booties (or hi top sneakers for that matter) gives my legs a bulgy look, and cuts into the front of my ankle when I walk. One of those instances where poor comfort and poor flattery align.
My own personal demon has been skinny jeans. I absolutely cannot achieve the relaxed-skinny look because my legs, especially my calves, are just too big relative to the rest of me. Every fall I get it into my head that I want to be able to wear big cozy flannels and long sweaters over skinny jeans, but then I do some try-on's and remember that this look is the exact opposite of what works for me, despite the fact that everyone else seems to wear it. Like Suz, I've also had to swear off tunics for the most part. I also have to exercise a lot of restraint with tall boots; because I don't have any skinnies to tuck into them, they end up being for use with skirts/dresses only, and, again, not as versatile as they are in other people's wardrobes.
Like others have said, I could see you in drapier white and denim blouses, rather than shirts. And maybe a black or olive anorak instead of a trench. I don't really see any of these as essential to your style -- it is, as you say, a question of how hard you want to work at making something work for you, finding the right version, etc.