How can I safely lose 80-100 pounds in 10-12 months?

I have been overweight since I was little. I was not and am not the type of person who enjoys being active. I know 100 pounds seems like a lot, but I weigh about 275-285 right now. My weight has been steadily creeping up since I was younger. I haven't been under 200 pounds in maybe four or five years. Next year is my senior year, and I want to feel and look better when it starts, and I know that I need to get started now. My biggest issues are that I am a huge procrastinator, I find exercise to be dull and quickly nose interest, I have trouble giving up my eating habits, and I have trouble motivating myself. I fear that by the time I decide to truly try losing weight, it will already be too late. I know that I can cut back on fast food and my mindless snacking, but what do I do about school lunch? The only decent option is pizza, fries, and a pop. I need serious motivation. Just telling myself that I need to lose weight hasn't been very successful.