Breakfast: two oatmeal packets. Or an oatmeal and some berries mixed in. Instant coffee with non dairy creamers and/sugar if that’s what you do
Lunch: something you can eat while moving. A couple cereal bars. Get the ones with the most calories per bar.
Dinner: pasta sides, Mac and cheese, pb&j sandwiches, tuna sides - if you’re fancy a Mountain Sides meal.
Snack: summer sausage, smoked cheddar, and crackers
If all of that is too hard, the US MREs aren’t too bad, although probably more expensive