Quick Healthy Snacks?

I weighed myself for the first time in months earlier, to find i have put on a lot of weight. due to eating a poor diet. I'm 14, and go kickboxing + football training and am going to start the gym and dance. But i don't eat a well balanced diet, i snack on big bars of chocolate through the day, with no breakfast only really tea. Does anybody havee any ideas for healthy food and snacks that i can take to school, but are easy to make ?