I sympathize with your back troubles. I have been on that roller coaster for the last 20 years and I am currently going through another episode. The thing that has helped me the most is the knowledge gained by going through physical therapy over the years. If I begin the manipulations learned, immediately at the onset of an episode, the impact is minimal. It is best used as maintainence and incorporated into your daily routine. BTW, I never injured my back carrying a pack. It usually happens doing something stupid or routine like folding laundry.

I also agree with Glenn's assessment about dropping the fries and not allowing them to convince you to "Supersize". It is very difficult to eat healthy during the day for many people, and just by eliminating the worst part (fries, sodas, sweets) you can keep it manageable. I have had some success using Cliff bars or even a Pro Bar to substitute a whole meal 1 or 2 times a week.

No matter which means you choose to lose weight, it has to be sustainable and a wholehearted lifestyle change. The one thing that is guaranteed is that, if after you lose some weight, if you return to your old habits, the weight will come back with a vengence. That's why most of the fad diets are not successful because they are not sustainable.