One thing that is helping me alot, is preparing what i take to work with me and sticking to it through out the day.
I used to work at mcdonalds for over 5 years.. and granted maccas is alot unhealthier than a bakery. the same principle applies i guess.. you work around food, and the convenience of just having it there is very tempting. At the job i am at now, i never used to take lunch, and i would go down to the local take away shop for lunch.. bad idea! i started making my meals the night before, got a visual image in my head of what i would eat for the next day and made sure i would take it to work with me!
Im taking a wild guess and say.. your 17 and living at home with your parents that cook dinner for you? if thats the case.. perhaps ask if they could cook just a little extra and you can put it in a tupperware container and take it with you the next day
Take lunch with you, it will make a big difference