You have a kid, or remember being a kid. What are or were some of his or her or your favorite things to use to dress up for playing? I don’t mean real costumes. My favorite were two sheer white (well, they started out white) synthetic curtains Mom let us have when they got too ratty to mend again. We used them for togas, princess’ trains, mysterious diaphanous veils on wizards and fairies and such, uncrossable (unless you leaped really really far) raging rivers, etc, etc. Also, my 5 feet of white cotton package string laboriously colored yellow using Mom’s highlighter pens, which was actually my Golden Lasso.
was mary poppins for weeks after seeing the movie.
raided mom’s closet for a long skirt, some hat or other i can’t recall what it looked like now, and an honest-to-goodness carpetbag.
once i got hold of an umbrella, i then practiced flying: by leaping off the staircase landing. 
after her initial heart attack, mother put a stop to THAT right quick.
I can’t really think of anything I wore for the moment, but I cracked up when my 5 year old came in the living room a couple of months ago wearing nothing but two washcloths, tucked into the front and back of her underwear, carrying a piece of the plastic piping from my laundry bag hanger thing that she’d tied a rope to. She was an Indian brave and that was her bow.
I had a Cinderella book with a picture of one of the stepsisters wearing what I considered the most beautiful purple dress. I used to wrap myself in a towel and “play Cinderella”, which consisted of going about my usual kid business, but wearing a towel. One of the neighbors’ grown daughters heard of this and gave me a purple velvet dress which she had outgrown! It was nowhere near to fitting me either, but I pretty much wore it every day after that for years (indoors).
Cowboy boots and a little vest with bucking horse appliques on it. I wanted to be a cowgirl.
Or… her horse. My grandma would give me a white towel and I would tuck it into the back of my pants or shorts as a horse’s tail, and I was suddenly a wild palamino mare!
Imagination was a wonderful thing.
In my tightie-whities, with a towel as a cape, I was a superhero! We also had an old wig of my grandmother’s when I was a kid, that I’d stick on my head along with the aforementioned and be Wonder Woman. A completely obliviously risque Wonder Woman.
Grease the movie came out when I was 10. We spent the next year (at least) wearing circle skirts, oxford shoes and wearing our hair in a ponytail surrounded by a scarf. I loved being a 50s teeny bopper!
Swim mask.
I was Jacques Cousteau!
The old underwear on the head. I don’t even know what I was pretending, just that I liked to walk around with my underwear over my head, peering through the leg holes.
Can’t remember too many specifics of what I wore, but did anyone else line up their kitchen chairs and drape blankets over them to create a rocket ship?
Yes, I did. But we played stranded in a snow storm instead.