If you are going to heat water for coffee or tea, then it is not much trouble to heat enough water to make oatmeal, as suggested above. Garnish it liberally with dried fruit, nuts, seeds and maybe a dash of brown sugar. The milled "quick" oats cook a bit faster than the whole oats. There you have a good breakfast.

If, like me, you prefer not to heat water for breakfast, I suggest eating granola or muesli (muesli would be more available in Sweden) and some powdered instant milk granules that will dissolve well in cold water.

My experience has been that I can hike all morning on a breakfast based on oats-plus-nuts-plus-milk and not get hungry again for 3 or 4 hours. Other whole grains might work as well as oats, but oats just seem to go well at breakfast.