i play piano, along with guitar, bass, tuba, sax, yada yada....
ya know what is the easiest way for me to play piano live, and able to hold my own in any song/jam situation? Use that transpose button, and learn to jam in both C major and minor. From there, you ask the gutiarist what key the song is in, you drop/climb enough half-steps to get there, and then you just throw down the pentatonic or major scale on the song. You can't fail.
don't get me wrong, there is nothing more beautiful than sitting home jamming 'sister christian' or 'i aint mad at you-2pac) in the correct key. But in terms of a working band, transpose C and major/minor will save your ass 99% of time.