And the OP is a tourist. And although I've been claustrophobically-unimpressed there when it is quite busy, when it isn't, it is a decent stop. And I'll stand by my Mezcal comment!

I'm always a bit wary of the places that end up on the "food tour" circuit or get too much publicity after some TV or other media hype. That said, Somebody Feed Phil has had me eating more than a few delicious bites. I give high props to Panaderia Rosetta (both the take out pastries and the cafe) and unless things have recently taken a nosedive, should be on anyone's food tour, and same to her Rosetta restaurant (although the recent World's Best Female Chef ranking might make it a quite difficult reservation), which to the OP's requests, is lovely and casual and reasonably priced on a world standard, despite its pedigree.

And really, a dip of a freshly made El Moro churro into some delicious chocolate is a snack that you can't beat.