Not a bad idea, but a lot of those "light" products just trade one thing for another, and sometimes you just end up with worse things ("light" sour cream has low fat, but much higher carbs than normal sour cream). If you want the most healthy dressing, just mix olive oil and vinegar. I think that I normally do 2 parts olive oil to one part vinegar, but different people have different tastes.
As for general suggestions, x2 to what Ltown mentioned, especially the grilled chicken. If you get 5 or 6 and cook them on sunday, then you have lunches for the entire week. Just put them in individual plastic baggies in the fridge, then you can pull one out in the morning and heat it in the microwave and throw it in your lunch bag (tupperware or alum foil will help it stay warm). Tuna in the pouch is very easy too.
Name some of your favorite foods right now, healthy or not, and then we'll try to find some common ground so you can eat things you like and still get fitter.