I think the idea behind the list is for basic things that you had to buy. Some of these lists are from the LDS Church, and many plant gardens, have fruit trees, and would can the fruit and veggie items. It is also assuming a stringent budget to build the storage, and tuna is probably the cheapest. Many times I have read that a year's supply is their minimum recommendation. Remember this is a list for 2 adults to "sustain life" for one year, and to double it for two additional people in the family.
I wouldn't want to eat that much tuna, either, but it seems that at least once a month Walgreens has other canned meats on sale, though more expensive: Celebrity hams, 10 oz Hormel roast beef, canned corned beef for $1.99 -- their normal price is around $2.79 here. Other weeks they have canned salmon, tiny shrimp, I think clams and sardines. It would just take longer to build the stash if you limited yourself to the $5 or it would cost more money.
In any case it is always good to have food stores for lean times or emergencies. You may want to change what you buy but it's a good guide to start.