You only need to carry your combo card and your passport. However, be prepared to be sent to secondary inspection every time you use the combo card.
If you're especially nervous, you might want to bring a copy of your I-485 receipt notice and a copy of your I-130 receipt notice or approval notice. However, those additional documents are not actually required. If they ask you why you have a combo card, just explain that you've applied for adjustment of status based on your family member. They should be able to look up the details in the system.
No one on this forum has ever been denied entry on a combo card as far as I know (and there are other members who have been here much longer than I have, who will tell you the same thing).