To boost calories and flavor I often bring...butter.
My 573 kcal oatmeal recipe is:
1/2 cup instant oatmeal (140 kcal)
1/2 cup non-fat powdered milk (120 kcal)
2 tbsp butter (200 kcal)
1 tbsp brown sugar (48 kcal)
1/8 cup raisins (65 kcal)
1/8 tsp salt (o kcal)
pinch cinnamon (0 kcal)
At home, in a Ziploc bag, combine all ingredients (make sure the butter is covered by the oatmeal and milk in case it melts a little). On the trail, bring 1 cup of water to a boil, add mix, stir, bring to boil again while still stirring, remove from heat and let sit for 5 minutes in cozy with lid.