When I did SYC I allowed for "gear" purchases since I knew I might need new runners during that time.
I did SYC to see if I felt I had "enough" clothing and wanted to learn to remix and get creative so I didn't allow *any* shopping for 3 months. (I did go on a bit of a buying spree for Boxing Day which fell right before my SYC started on Jan 1.
I struggled a bit here and there and made the odd purchase during the time (and felt guilty about it too!) but am very happy I completed it. It has changed how I shop and how I view buying clothing dramatically!
Think of the *reasons* you want to SYC and then make up your own rules. Post your rules (for accountability) and invite others to join you.
Not me though, 3 months in 2011 was enough for a little while! LOL