In my opinion, the K&B book is all
you should need. At least, that's all I used. I believe they sell a separate book of just mock exam questions. If you don't own that one, I think it would be a good purchase.
Another fun way to get some of the basics is to play the
Rules Roundup Game. It includes some topics like bitwise operators that are no longer on the SCJP exam but it's still fun and valuable.