The test for emergency food is not nutrition. It is whether you can eat it with no electricity, no gas, no water and no refrigeration.
Buy what you already eat. A cupboard of unfamiliar rations goes out of date untouched. Tinned fish and beans, rice and pasta if you have a way to boil water, oats, nut butter, dried fruit, biscuits, long-life milk, tinned vegetables.
Rotate, do not stockpile. Buy a few extra of what you use, put new at the back, eat from the front. This is the only method that survives contact with real life, and it costs nothing extra over a year.
A tin opener that is not electric. Households discover this omission at exactly the wrong moment.
What the household actually needs. Baby formula and baby food if there is a baby; the specific things a person with a medical condition needs; pet food. These have no substitute, and shops run out of them first.
The freezer. A full freezer holds its temperature far longer than a half-empty one. Keep it closed, and eat from it before the cupboard.