I had to do this 2 weekends back for a German/American Fest.

In advance, I had practiced a handful of ethnic standards that I thought would be recognized and liked by the listeners and stored them in registrations on the PSR3000.

They liked the selections TOO well. They wanted more, and more...
Because a good friend of mine put this bash together, I wanted to try and keep the people happy by giving them more of what they wanted. I pulled out a fake-book-styled ethnic book and started playing tunes one after the other, songs I had never played before.

I went for broke and the results went amazingly well...
On the PSR3000, all I did was select the rhythm that fit the song, pressed the OTS (1-touch settings) buttton and used whatever sounds + accompaniment were programmed to the OTS... While in the middle of a song, when I wanted to change the melody/lead instrument to be something other than the 4 OTS selections, I just pressed the 'freeze' button to prevent the rhythm/accompaniment from changing on me, and pressed a different registration button that had a voice/instrument that I wanted to use.
Fast and simple.