I would not use any other shampoo products than the keratin products. They sure don't give you too much shampoo and conditioner in the kit. As stated, I use the Brazilian Keratin shampoo and conditioner from my old treatment and it works great. It cost $50 ea. for a 32 oz. shampoo and conditioner, which should last you a long time.
This is the company I order my shampoo from: http://www.braziliankeratin.com/
I also noticed the beauty supply store that I buy from carries this product.