Hi Iya,
For my wife's K3 interview (I know yours is K1, but as far as evidence of a real relationship they want to see the same things) she brought the following things:
- Pictures of us together from both my trips to Russia
- Transaction history of my calling card account for the time since we met (1 year). I don't think this counted because it didn't show the actual phone numbers called
- Copies of my cell phone bills which showed records of incoming and outgoing SMS messages. We texed each other about 10 times per day each for the last year, so we had 60 pages of records even in a tiny font
- Greeting cards which I had given her
- Most of our emails for the past year
- Emails to and from my other family members (mom, dad, aunt, grandparents)
- A copy of our wedding invitation for our upcoming ceremony in the US and pictures of her dress
That's really about it. The consular officer didn't even ask to see the phone records or emails. He had a copy of my affidavit that I submitted with my I-129f that told the story of how we met, and he mostly just asked her about how we met and made sure the story was the same. He picked out a few of our pictures and asked her to talk about them. He also looked at our wedding invitation.
I hope this helps and my wife and I wish you the best of luck!!