Pack around the whole outing
Include the journey to the start, the walk itself and the trip home. If you will be away over lunch, arrange lunch. Bring a reasonable contingency for delays rather than assuming you will finish at an exact time.
Keep the planning specific. A short marked walk near a town is different from a remote route. For demanding trips, follow outdoor guidance appropriate to the route and your experience.
Choose a mix of familiar foods
A sandwich, fruit and a wrapped snack may each be useful at different stops. Choose things you know you enjoy and can handle easily outside. Follow storage directions, particularly for perishable foods.
A protein bar is not a complete food strategy for every walk. Consider the amount and variety of food across the day, rather than focusing solely on the protein number of one item.
Organise the bag for real stops
Keep an easy snack accessible so you do not need to unpack everything. Protect food from damage, and separate it from wet clothing or equipment. Bring a place to put wrappers and leftovers.
If you are walking with others, avoid assuming they can share your food. Ask about allergies and preferences first, and keep labels available. Henry contains egg and almonds.
Treat water as its own planning task
Bring an appropriate drinking plan for the route and conditions. Do not rely on finding a refill unless you know it will be available. Food and fluids solve different needs.
When you return, check what worked: enough food, manageable portions, no awkward preparation. Use those observations next time. The best food bag is one that fits the outing and leaves you free to enjoy the walk.