No codes needed in this purchase! You just have to make sure you have the right items. I have collected a few items that it works for. You just have to make sure you have 4 items in your cart. It has to be the $4.49+ one and not the $2.98 one. Yes, both brands can be mixed. I'm loyal to Aveeno, so I will be out for this deal.
No, you can't do this deal in store; it won't stack (but I haven't tested it). This is [pretty much] free if you have previous giftcards to use. For example, the total is $20, but your giftcard is $10, you pay $10, but you'll be getting back $10 in giftcards. I wish I saved my giftcards more to rollover these.
Head & Shoulders.
As always, use ebates: http://www.ebates.com/rf.do?referrerid=eIGVjyxRwYX2D2nPq6XrVA%3D%3D&eeid=28187
**New users will always be prompted to choose a giftcard when you create a new account.