Eating before Shabbat Midday

Don't fast on Shabbat (except Yom Kippur!) past halachic midday:     
  • If you will not finish shacharit before halachic midday, you should eat or drink earlier in the day, even before you begin shacharit—water can be sufficient for this purpose.
  • If you will finish shacharit but not musaf by halachic midday:
  • Finish shacharit,
  • Make kiddush,
  • Eat some mezonot, and then
  • Return to say musaf.