Exchange student I’m hungry

My host family I decent and they give me 3 meals almosy everyday except if for example where eating out they want me to pay and I honestly thinks it’s fair enough, the only problem is that sometimes I’m still very hungry after the meals and I simply want to eat more, I’m 16 175cm 60kg and I’m in my growing phase so I’m constantly hungry and my host family doesn’t really like me eating more than the 3 meals they provide, so im constantly looking for food and I’ve been using a lot of money this exchange simply just for buying food, and it’s getting very expensive, anybody know some cheap food that I can eat easily? Or stock up on? Or some food that keeps me full?