Tfw you’re an Dutchy and simple home-prepaired sandwitches (read two slices of bread with some butter and cheese between them, nothing fancy), are the countries national breackfast and lunch. Warm food is for dinner traditionally 🤣.
Either way, sandwitches (no need to limit to peanut butter, a lot can be put on bread!), salads (pasta or normal), fruit, veggie, cheese, and certain type of meat (like smoked or dried sausage, or beef). They all make great parts for cold meals you can keep in your bag till lunch (speaking from experience). Some cheese & meat are even packed per small packages for easy take along as snack usage.
I would suggest you do go to restaurants a few times, just to try the local cuisine (or their variation of other cuisines). But it probably will be expensive for you indeed. Whenever I’m in Asia, I feel rich (and I’m really not). Even Japan, who is often said to be expensive, is cheaper than my country. Especially when it comes to food.