Do JRFs have administrative responsibilities within the college? Or is it pretty much all research all the time, with the option of a little tutorial/supervision teaching?
Depends. Chances are you'll be put on various college committees, which may or may not be onerous. As for whether teaching is an "option", if you're in a rare field, you may find yourself pinned with being director of studies whether you like it or not. It's very unlikely you could opt NOT to teach at all.
Does "free meals in college" indicate that each individual college has its own cafeteria-like setup, and that I would go to my college specifically for these meals?
Yes. Your meal allowance will be for a certain number of college cafeteria meals, or formal dinners.