According to my experience, some simple and low cost foods rally keep me energetic. Eating oats with banana or peanut butter in the morning does not feel heavy, but keeps us satisfied for a long time. Eggs are easily available protein. Rice, dal, and vegetables together give energy at low cost. Curd is very helpful for digestion. Eating banana or guava every day instead of junk food gives energy. Eating roasted peanuts or chickpeas in the evening snacks makes you feel active without fatigue.
Really these simple foods kept me healthy. My advice is, don't start everything at once,if you start one or two habits, you will gradually see the difference.