In many developing countries you can get a meal at a street kitchen for a $1-2. That’s probably way less than anything back home if you are from a western country.
This is a great place to save money on food. This is where many of the locals do their shopping because it’s the cheapest. Ask your host for recommendations.
Cook your own food
If you really want to save money on food this is the way to go. Especially in more expensive countries where eating out 3 times a day quickly adds up. Cooking your own food is often the cheapest money dependent option. You can join up with other people at your hostel and cook together. It’s nice with the company and you all share the work load while having a great time together.
Choose accommodation with breakfast included
Often the included breakfast is very basic but it might be enough for a few hours and it saves you money on breakfast.
2 meals a day
In countries where food is expensive you might consider eating 2 meals a day instead of 3. In between meals you can eat some cheap snacks to keep going if you get hungry. If you also stay at hostels with breakfast included it can really help you save money on food.
A lot of perfectly fine food is being thrown out all the time, particularly in the industrialized countries. It’s usually still wrapped in its original packaging and neither old nor bad in any way. 40% of the food in the US is thrown out, and they are not the only ones. So, go for it!
Food does come from nature to begin with after all and not from a supermarket even though we might forget that sometimes. It’s possible to seek out places with a lot of fruits and vegetables and keep it as a base to travel from. Usually that would be outside cities, but urban gardening is getting increasingly popular. Surviving only from what nature provides is probably going to be difficult most of the time so still a bit of money (or dumpster diving) might be necessary for supplementing.
Of course this isn’t possible in cities, but if you like camping, if you are doing a road trip or long treks this might be an option for you. Just check the laws of the land first.
Keep in mind that the links provided are not exhaustive. It is just a place for you to start, and if one site doesn’t provide the information you need keep looking for similar sites or use your creativity to find alternatives. You can also simply ask either here or at a travel forum. I merely showing you a small glimpse of what’s possible.