So there are many different ways to approach food.

Saltine crackers could be paired with other things like you said, peanut butter or maybe canned tuna/salmon but alone, they do nothing for you.

Along with peanut butter, tuna and salmon you can also buy sardines which are very nutritious if you can stomach it. Also, people pack ingredients for “moose goo” which is peanut butter, rice flour and honey wrapped in a tortilla.

Ingredients for a trail mix might not last long but it gets the job done.

MREs are an option.

Meal shakes like Soylent, Garden of Life and Huel are becoming more popular.

Freezing lots of meat for later

Potatoes are considered the number one survival food in space.

Ramen may not be a bad option as you it lasts a while and you can mix chicken or tofu in for some nutrients.

Most of things do require you to boil water, have access to a freezer or climate controlled storage so it basically boils down to how far down rabbit hole you want to go.