When Princess started to charge for some of the dining rooms, it upset many people.
On the Ruby Princess, you only have one causal food place. It is called the Salty Dog Grasto pub. This is in the Wheelhouse bar on deck 7 and is only open from 6 to 10 PM.
Here is the menu for the pub-style food.
It was suitable for being the only casual dining place on the Ruby, but it was a busy place. So, if you want to try this out on Ruby, I suggest it.