Hi Arua,
I'll try to build on the helpful suggestions offered by my colleagues. To summarise so far the recommendations have incuded:
1) Eating at regular intervals (2-3 hours)
2) Eating 3 meals and 2 healthy snacks per day if possible
3) Eating foods containing slow releasing enrgy (wholegrains, root veg, squashes etc.), healthy fats (oily fish, nuts, seeds, avocado etc.) and protein (lean meat, fish, eggs, dairy, nuts, seeds etc.)
4) Bulking out dishes with plant-based protein i.e. beans and lentils.
5) Planning and preparing food in bulk, batch cooking, freezing.
6) Slow cooking soups and casseroles
7) Preparing portable nutritious snacks i.e. oak cakes with nut butter, fruit and a handful of mixed nuts etc.
8) Sourcing good value produce - i.e. frozen berries, canned/frozen fish, discounted supermarket goods etc.
In addition I would suggest to save time and money, make the most of any 'left-overs'. By cooking extra in the evening it is quick and easy to add cold-cuts of poultry or poached fish to a mixed salad/rice salad/quinoa salad for a nutrient-dense lunch. Also try to eat seasonal fruit and veg as it tends to be locally grown and cheaper making it better value. This will also increase the diversity of the food that you eat which may benefit your gut and overall health.