You see, the shelf life of that freeze-dried stuff actually isn't nearly three years. It would get the crew by on the 6 month trip to Mars, but that's about it. Not to mention, it would take up a lot of precious space and cargo weight to carry three years' worth along.
According to Discovery News, current foods lose their nutritional, visual, and flavor appeal by the first year at best. That same article outlines new technologies being researched for foods that would last 5 years in lighter-than-ever packaging.
Another approach to making Mars possible is providing for astronauts to grow their own food and fibers (toilet paper and other paper products) once they reach Mars. This would be done hydroponically in special greenhouses and would utilize waste produced onboard. From The World of Food Science: "A menu of main courses made up of casserole dishes with the protein base alternating between tofu (from soy beans) and rice and beans, served in Spanish-style tomato sauce seasoned with ingredients from salad crops (green onion, bell pepper, etc.) was chosen as a suitable type of meal entrée that would meet daily requirements for macronutrients, while micronutrients would come from consumption of salad crops accompanying each meal entrée.".
What do you think? Would you go for the prepackaged salmon or self-grown rice and beans? We find it interesting that when all is said and done, making Mars work comes down to our basic need for reasonably appealing food!