I'd love for them to play a really obscure released song, or something they've never played live.
Songs that were recorded during album sessions but showed up elsewhere would be ideal.
Sessions, There Goes Everything, Goin' Down to New York Town, Sunday Morning LA, BIABSN. Any of those would be incredible. I absolutely love each of those tunes. It's a shame they've never played any of them live, to my knowledge, at least.