We absolutely will not be shipping containers of food to Mars.

We absolutely will be. You have no concept of the amount of energy and resources needed to feed a single human being on Earth for one meal, let alone a whole colony on another world without a breathable atmosphere and possibly toxic dirt for an indeterminate time. Farming under the best of conditions is extremely energy consuming, then there's the need to either import hardware from Earth that is specially made for Mars or go old fashion and do a lot of it by hand. There is no where else in the solar system where you can just throw seeds at the ground in large enough quantities and feed whole cities. I do homesteading, my dad tried to be totally self sufficient foodwise when I was a teen. Guess what? Turns out that's really, really hard to do. And that's under the ideal conditions of Earth.