Some of the comments above reminded me that what you eat the night before is pretty important, certainly plan to eat well! On a multi-day trip, we tend to have quite large evening meals, good old spag bol or other pasta, chilli, curries etc mostly, but seem to easily burn off the calories! Also make sure you're well hydrated before you start, not just whilst on the hill, so if you have a few drinkies the night before (it can happen
) drink plenty of water before bed and plenty of liquid in the morning.
Breakfast wise, as I'm often on holiday as opposed to just a day trip, regular bacon sarnies feature strongly, but I normally also eat some cereal, plenty of orange juice, and perhaps a banana at the start of the walk.