Well, if you have the money, want it to be easy, and like to start walking late, together with everyone else... take the breakfast included in the demi pension.
Personally, I thought it was far too expensive for what you get and also preferred to start walking earlier than the French, to have a bit of alone time in the mornings (walking through the early morning fog, magical!)
You can buy a jar of confiture (can fill it into a more light weight plastic container if you want to) or some cheese, butter, instant coffee ect. to carry with you. It's not as heavy as you think. Baguette is available almost everywhere, but for sundays/mondays maybe carry an extra one just in case. Fruit cake, madelaines, hard boiled eggs, yogurt ect are also easily available options... whatever you prefer.
That way you can have a much cheaper breakfast, and at the time you want.
Your choice!