I could go a couple of days without a shower, but I can't go that long without washing my hair. It is disgustingly oily. I shower one morning, and it its oily 24 hours later. I remember going out once without having showered and my friend stopped me, pulled me aside and said "Kay, what did you put in your hair?" Or as a teen, when I hadn't taken a shower by noon, and I would later announce I was going to do so father would tell me that "It's about time!" He was also the first to point out when my hair was oily.
From what I have read, your scalp is supposed to calm down and stop producing so much oil after you stop using regular shampoo and stop washing everyday.
But... But... how do you survive the transitional period???
I think I would have to become a hermit.
Dry shampoo. There's a few in regular stores, advertised for use after workouts and one from lush(if you can get it) They soak up the oil and then you brush it out.
Yes. Even plain cornstarch will do in a pinch. What I found most useful, though, was getting a 100% boar bristle brush, which distributes scalp/root oil down the length of your hair, eliminating "grease clumping" and gets rid of any fuzzies or dust you've picked up over the course of the day.
You don't have to spend a whole bunch, I got a Goody brand one for about $7 at my local drugstore. If you've never used one before, it'll be a little strange, since they don't really "penetrate" the hair to detangle and whatnot like a normal brush. De-tangle first, then brush at night from root to tip. I have to work in sections and follow the brush with my hand to cut down on frizzies. Once you've done this, you're going to look pretty gross at first, because all the oil near your scalp will have been spread out along the length of your hair. In the morning, though? Once it's had a chance to sink in? Heaven. My hair looks shiny and conditioned all over, instead of looking "normal" on the length then super greasy near the scalp.
Make sure you wash your brush regularly, though. I do mine the same night I wash my hair, so every 3-4 days.