Just to be clear, did you want the tunes as sheet music to read from for playing on an instrument - or did you want the tablet to actually play the tunes through a PA system?

If it's the latter, any smartphone or an iPod would do that for you. If it's the former, then there's quite a choice. I tried putting chords for tunes (as PDF documents) on to a Kindle, but it's not very good away from a good light. Perhaps an iPad or something similar might do the trick - but I would never rely on a battery, even a full one, on a long gig. Always have a power lead with you!