If I lay off the chocolate, candy, soda etc...?!

Everything you eat has certain types of acids and dyes in it which can, over time, stain your teeth. The only thing here that would help drastically to stop doing would be soda - It can corrode your teeth significantly, and then the shade won't be the only thing you'll have to worry about. It's nearly as damaging to your teeth as battery acid. (Here's a list of the corrosive levels of some common drinks and sodas, as compared to how corrosive battery acid is: http://www.fitsugar.com/Case-Youre-Still… )
Drinking soda regularly over long periods of time can corrode the teeth to a point in which they do not look unlike "meth-mouth."

There are certain types of things which have stronger chemicals in them which can stain your teeth - It's not necessarily all in junk food, either. For example, coffee. Also, cigarettes. People who use these two things regularly for long enough usually end up with stained teeth. It would be rather difficult to eat right and keep your teeth completely unstained at the same time. So long as you brush and floss right, I wouldn't worry too much about most of it (besides the sodas).

Yes, candy has an awful lot of sugar in it, which of course can cause cavities. However, I'm not sure if that's the same thing as saying it will stain them. Probably not. Either way, you can not keep your teeth perfectly white simply because there's lots of things which can stain your teeth over time. However, you can ask about whitening treatments at your dentist's office, or you can make sure to ask him or her what you can do to help keep your teeth white.

Hope this helped.