Dave Grohl, Krist Novoselic, and Pat Smear played several songs with McCartney. They started out with the song that they recorded when they first jammed together. Cut Me Some Slack was featured on the soundtrack for Sound City which is the documentary Grohl produced about the studio where Nirvana's Nevermind album was recorded. They also stuck around to play several Beatles songs and a Little Richard cover (which was covered by The Beatles).
McCartney and Nirvana made headlines when they played the 12-12-12 Hurricane Sandy benefit and Saturday Night Live back in December. This is the first time they performed multiple songs. Of course, many may think its less of Nirvana reunion when Dave Grohl plays guitar.