This is probably a dumb question and one that will be answered in my book when I get it, but what do you do for breakfast? There is no way I am carrying and cooking my oat porridge with me, but obviously breakfast is going to be the crucial meal in the day.
Whilst it is possible to buy porridge oats and other cereals in supermarkets I've never seen porridge available for breakfast in Spain and definitely not in the many little bars which provide breakfast in the rural stretches of the routes. Coffee is the staple at breakfast either with milk or solo - and for many workers topped up with a tot of spirits and of course a cigarette! Lots of Spaniards eat sweet things at breakfast time and most bars will have cakes and biscuits - the ubiquitous Magdalenas. Toast is sometimes available or simply bread with or without butter and jam - mermelada is the word for jam - there is no word for marmalade. For some, toast with a little ham and cheese works well.Some Spaniards will have toast liberally sprinkled with olive oil and salt. Bars will also have either freshly squeezed organge juice or bottled "fresh" orange juice. Although every bar serves coffee - everything else is optional - I find myself buying fruit and keeping it for breakfast or even a spare bocadillo. If you take your own herbal tea bags they will happily give you boiling water and no doubt will be interested in the brew! Different from home - but I've never gone all that hungry yet in Spain. Goodluck
Just in case I can't find an open bar or bakery, I usually carry chocolate, muesli bars, bananas, nuts and dried fruit and a packet of light, sweet bread rolls. Also useful are the 'long-life' packs of yoghurt drink, which does not need refrigeration.
I have seen pilgrims boiling eggs in the albergues for breakfast the next morning. And if the albergue has a fridge you could buy some cheese and salami to eat before walking.