Curt,
I have used an ipad. I convert the songs to individual wavs and they can be played in Garage Band or another program is Multitrack. In either case like the idea of being able to control each instrument/track.

If you want simple, export each song to one wav file and put it in iTunes and set up a folder for each set.

Once I tried exported each song to a single wav and then transferred the songs to my Boss RC3 loop pedal via USB cable. That thing can hold a ton of songs. The instructions in the pedal's manual list how to move from song to song. Worked pretty good but you need to get the songs set at the same volume before you move them to the pedal.

For the ipad, I purchased a Alesis I/o dock. It has a left and right out which I ran to two seperate channels on the board, panned one left and the other right. Nice stereo sound. I also set and armed two channel in the program I was using (multitrack at the time) which created live effects for my vocal and guitar. I could then blend myself with the other tracks/instruments. If you are by yourself, you can hit record during your sound check, lay down a song and then walk the room as you play it back. If you adjust the levels they will remain the same when you play live. Only concern... you need to do this for each song.

Hardware solutions such as the loop pedal are the safest. I always have a back up on my iPhone for each song. Technology has a way of failing when it counts most.

I am now working with Ableton live, which is set up mainly for this purpose.

Just my two cents.