He hugged McCain onstage and called for Americans' help "in making this bipartisan dinner not just an inaugural tradition, but a new way of doing the people's business in this city."
Throughout the day, Obama showed no hints of nervousness about becoming president within hours.
"I don't sweat," he told volunteers at Sasha Bruce House, a shelter for homeless teens in one of Washington's poorer neighborhoods. "You ever see me sweat?"
All day, he switched easily from self-deprecation to faux cockiness to calls for action.
"Make sure I do something simple," he told Sasha Bruce organizers. "Don't give me plumbing or electrical work."
As he painted a wall with a roller brush, he quoted King as saying, "Everybody can be great because everybody can serve."
"Right?" he asked the late civil rights leader's eldest son, Martin Luther King III, who was almost overlooked while painting nearby.
"Right," King assured the president-elect.