Huge subway fan here. I ate there almost every day during the summer. That 5 dollar footlong that's a subway club is INCREDIBLE.
Some RobFunk tips: Stick with your primary cheeses: provolone, american & swiss. Don't even waste your time with cheddar unless the original recipe calls for it.
Don't waste your money on extra cheeses or meat, the sandwich is fine without it. Don't bother with green peepers, cucumbers or Jalapeños. All other vegetables are good, I get extra; it's like having a salad in a bun.
I tend to stay away from the pre -cooked stuff (with the exception of tuna), stay with the DELI MEAT sandwiches. Light mayo and chipotle are good for sauces, and I almost always get oil and vinegar.
When it comes to bread: believe it or not, the plain white is the lowest cal, the wheat is the healthiest and this will shock you: the wrap actually is actually the worst in terms of a health choice because of the fat in the oils (although I DO like the wrap as someone eluded to above). My fav is the Italian cheese.
Alright that's with my subway rant. Love the place, have been there so many times it's silly. Hope this helps someone out.
I tried a lot of stuff there though.