The landlady’s kindness has nothing to do with being wasteful, except in the sense that your fellow students appear not to be mature enough to handle the freedom they are given by the landlady. They appear to still need a parent to tell them what to do. Write your parents a letter and thank them for doing a good job raising you because you are being responsible while living away from them. As to your fellow students, set a good example, but you probably will not be able to influence your choices too much because having a peer lecture you is usually resented.