Do you have photos of the two of you together over the past 2 years? How about travel receipts, like air tickets for shared vacations,
hotel receipts, photos of you with each other's family?
Affidavits from family afirming your relationship are also usually helpful.
If your ID was ever entered into the system by CBP, there may be a record, but if you're driving and don't have a passport, there's not many ways they can record your comings and goings.
You WILL definitely need to get yourself a passport before you go for your interview at the consulate. They will have to put your K1 into your passport. NO way around that at all. And you'd better do it quick, as there may still be a backlog, considering the new passport laws to be enacted early next year.
For more info on marriage based immigration to the us see
http://www.visajourney.com