I went out and purchased a few compilation albums (101 80's Hits, 101 90's Hits, 101 00's Hits etc.) Best investment you can make as a mobile DJ. If they said they don't know/mind "as long as its good" (Which I've had a couple times) you've got, literally, hundreds of songs that will be known by 80% of the party. Worst case scenario, let them look at your playlistism and let them pick. You're not doing clubs yet so requests are sort of mandatory