Aluminum foil can not only limit to food, it can also be used to put on windows to keep the house cool during summer and hot during winters.
An aluminum foil keeps the food warm, but placing the foil directly on the object or food doesn't help much. The reason behind this is, if the foil is in contact with the object, the thermal energy would move in the foil itself and might get away, but if the foil is placed a little away from the food then it can properly reflect back the thermal energy and maintain the freshness of the food. So to avoid contact between foil and food, you can add a few layers of butter paper to make air pockets and then add a pack in a final layer of aluminum foil.
As aluminum is a poor insulator (a substance that doesn't allow passage of heat) so to make the foil more effective, place it (food wrapped in foil) in fiberglass or ceramic tiffin boxes. It doesn't only keep the food warmer for longer, but also keep things cold. It acts as a barrier to oxygen and air which can transfer heat to cold or frozen food. The bottom line is it helps by maintaining the temperature of the food, be it warm or cold.
Aluminum foil should ideally be used only to keep food warm for shorter periods of time, but many people store the food for longer which may have consequences.
Aluminum foil locks moisture and odor in and keeps the food fresh but hot and acidic foods should not be put in aluminum foil as the aluminum will leach into the item.
For most working people, eating packed homemade food is the norm. All you need to do is give a little attention to how this food is packed and carried. Be Safe!