What did 3rd Party Accessories sell for on Black Friday last year (2011) at the Apple Store?
Go now and buy what you want would be my advice. If it subsequently goes on sale, go and ask for a price adjustment on Friday. (Don't wait till Saturday to ask, though) 

Apple's return policy is quite consumer friendly, so you could always not open things if you are on the fence and exchange or even return it until after the New Year due to the extended holiday season return policy.

Even if I had a list of things on sale - each store has different stock, different models so guessing which items will be in stock at your store will be hit or miss.

Also - Apple's announcement states that you can start shopping online at Midnight, so you can make your go/no-go decision well before the stores open on Friday. I would get the Apple Store app installed on your iOS device so you can shop, pay and not wait in line for items that they don't have stashed at the "rapid sales" line where many popular items are stocked in large quantities to minimize the delay of getting your item from the stockroom or finding someone free to sell you your new loot.