It all depends on your setup, and theirs.
If you want complete anonymity, a fresh iPod Touch, laptop or unregistered Droid wouldn’t have anything to share that was too useful. (MAC ID, browser info, etc.)
Many of these hotspots have a long disclaimer that requires you to click on something. That something may or may not be poking around. Frankly, the folks at the local Burger King or Howard Johnson’s don’t have anything terribly sophisticated.
You could set up a virtualized OS on a laptop, log in with that, and wipe it regularly... that would be quite safe.
What is meant by a “fresh ipod touch”?
I often surf with mine on public wi-fi while traveling.