First you are likely to face opposition from your friends who are addicted to junk food. they may even ask you not to interfere about their food habits as it is not related to you. for that you could aware your friends about the risks of junk foods by variety of techniques. you could tell and also show them that more delicious food can be prepared at home that are healthier as well as less money consuming. you could deliver speech and perform skits in your morning assembly programme. you could also take the help of your principal to strictly warn students not to bring junk foods to school.