what is the best kind of portable setup for doing 2 track live recordings?
For this kind of open recording, if you scratch "portable", you have a lot more choices, like mentioned above (R44, lapppy taping etc).
If you will have access to AC powering and a workspace where you can put your gear, you should definitely consider larger boxes.
I don't know what you consider portable, but a flavor modded UA-5 + suitable bit bucket (maybe MTII for 24bit) might be a cheaper combination than anything else mentioned so far. What's your budget?