TLDR;

1. The only way you'll learn the value of food is by DOING

2. If a food you're going to eat doesn't have a barcode then search for the next best alternative

3. Over time you'll be able to do this instinctively without MyFitnessPal

4. Be proactive and start scanning everything, just to make you aware of it's caloric value. This is especially beneficial when doing your food shop

5. This is a skill that you will retain for the first of your life