Answer: Duplicate of the Declaration of Independence
Ben says, "A souvenir. I thought it might be a good idea to have a duplicate, turns out I was right. Actually, I had to pay for the real one and the duplicate, so you owe me $35, plus tax." Abigail owes him the money for the duplicate because she loses it to Ian when she is hanging off the door of the catering truck. Ben being the great guy that he is, never actually collects the money from Abigail, probably since they fall in love by the end of the movie. The souvenir that Ben is speaking of is a duplicated copy of the Declaration of Independence that he buys in the National Archives Building's gift shop. The New England Current is the newspaper that Benjamin Franklin submitted the Silence Dogood Letters to, since this was the paper run by his brother. Franklin had pretended to be a middle-aged house wife in order to have his ideas published in the paper anonymously.