Refills are included at TS restaurants on things like juice at breakfast, soda, coffee, tea at dinner.
At some TS, people (including me) have been allowed to switch from soda with meal to coffee or tea with dessert. At some places, people have been charged for a second beverage.
Most CS (in the parks) do not have free drink refills. It has been reported that a few do, but I have not personally experienced this. Most CS at the resorts do have free refills.
I know that you can get milk, but I don't know if you can get it refilled.
I know that I got juice and tea at breakfast--no extra charge.