In Warsaw, the so-called Royal Way (the street name changes a few times) is the pedestrian only strolling area.
This may suggest to some that Nowy Swiat, the first leg of the Royal Way above Jerusalem Avenue, is pedestrianized - that is incorrect. Only the segment up near Castle Square is closed to traffic. However, Nowy Swiat, and Foksal, the cross street, is a very lively stretch at night, with numerous restaurants and bars - and a few very young and VERY friendly young women who apparently wanted to get to know me better - as I walked back to the Chopin after the opera one evening [and the opera is another good evening option, and it IS walkable from the Chopin - maybe just one way].
If you have the RS guidebook you will see reference to several food halls - Hala Koszyki is in Srodmiescie, there is a large bar area surrounded by a number of food vendors representing a number of cuisines and ethnicities - should be easy to find pizza or burgers. It is near Plac Zbawiciela, which I walked through - I thought it was a case where Rick was a bit overly enthusiastic in his description. But nice to walk around on your way to the food hall. You may want to take a tram or bus one way, as it's a bit of a walk from the Chopin B&B. Also very lively at night.
The other food hall I visited was Fabryka Norblina, which is near the Uprising Museum. If you visit the museum, it's a logical stop for lunch. I would take the tram at least one way - there would still be walking involved from the tram.
I didn't make it to the food hall at Elektrownia Powisle, but that could be another good option.
The Jakdojade.pl app is invaluable for rapid transit in both cities - either to buy individual tickets if you don't have passes, or to plot your trips. A 72-hour paper pass may be just as easy to use for fares.
In Krakow, one thing off the beaten path would be the blue kielbasa van - Kiełbaski z Niebieskiej Nyski - two guys cooking kielbasa over an open fire in the evening, working out of a blue van, I believe a bit west of Kazimierz [look on YouTube]. At Plac Nowy in Kazimierz, in addition to the zapiekanek windows [which I didn't try], there are also two rows of stalls with a number of food vendors, including one featuring grilled meats, with a very good grilled kielbasa.
For other food ideas for Krakow, try Planet Krakow on YouTube.