When homecooking, the most important thing to supplement is Calcium - bc it is needed to "balance" all the phosphorus. A multi is nice bc then you get vits A & E, which are often added to kibble.
The other biggies are the EFAs, probiotics, and digestive enzymes.
I use eggshells for the calcium (or you can use Bone Meal) and then I give this multi, which contains vits, minerals, digestive enzymes, EFAs, and probiotics:
http://www.onlynaturalpet.com/produc...at/999065.aspx