What a terrific thread, MYH! Thank you so much for starting it. I've just read all 13 pages, and now I'm ready to contribute, secure in the knowledge that I won't be replicating anyone else's comments!
First of all, about scarves and t-shirts: that is my basic uniform! About 5 years ago, I standardized on the Ralph Lauren cotton tees in white, black, and navy... plus one pale pink. I stocked up on the white and black ones when they went on sale; they have since changed the design. This is what they look like now (sleeves a little shorter, style a little slimmer, price a little higher

):
http://www.ralphlauren.com/product/...ab=ln_women_cs_short-sleeve&parentPage=family.
I live in Northern California and am now retired, so I usually dress casually. A black tee shirt or v-necked sweater, a casual jacket (if it's chilly), a black skirt or pants, or a denim skirt, and a 90cm. (Black with black... you can tell I'm a transplanted New Yorker!

) Most of my 90cm scarves are from years ago (I'm talking mid-1980s!), when I used to wear them to accessorize a navy business suit so I didn't look like a guy.

(Those were the "dress for success" days, when women had to look like men if they wanted to get ahead.)
But now I wear my scarves with extremely casual clothes, and I pretty much wear a scarf every day. Sometimes I take the time to make a complicated knot, but I usually just rely heavily on two of Mai Tai's rings: her Anneau Infinity and her horn Shawl Ring.
In the first picture, which I took today for SOTD, I'm wearing a black tee, a jacket, a denim skirt, and I just threaded the ends of the scarf in opposite directions through the Infinity ring. The scarf stays in place all day, no sliding around, and I can have it be as high or low as I want.
The second picture was taken yesterday. I had a meeting, so I dressed up a bit: v-necked sweater, black skirt, and the scarf in a criss-cross knot through the shawl ring. Again, easy-peasy: the scarf stays put, and I left it loose & large around my neck because it was a chilly day.
And the third picture shows that same scarf, on a different (much warmer!) day, worn over a plain white tee. I think I was wearing my denim skirt & sandals that day. I made the bias fold a little thinner, because I didn't want it to come up too high around my neck.