Does anyone code on their tablet to go? What do you use?

I've started commuting via bus and will soon be commuting via train and am finding myself spending time or wondering about small problems on my iPad from time to time. It would be nice to have a ruby interpreter or irb right on my tablet to muck around.

I could use my laptop, but it can get bulky whipping out a 17" mbp from my book bag while sitting next to someone to test something out. Any of you guys coding or looking at code on a tablet?