A few of our store cupboard basics are
nuts: walnuts
Seeds: sunflower, pumpkin, chia, linseeds
Sun dried tomatoes
jars of olives
preserved lemon
tins of tomatoes
tinned sardines
olive oil
various vinegars
capers
These are all the sort of items which brighten up basic foods. For example, today we had an omelette for lunch, which had a few strips of sun dried tomato in it, along with grated cheese. I often add a few olives to salads and sprinkle some seeds over the top. You need to find what excites you, taste-wise.
Personally, I would start with a meal plan for the week, trying to dovetail items (e.g. roast chicken on Saturday, leftover cold chicken for Monday lunch, homemade chicken soup on Wednesday) and then make up your shopping list from there.
We almost always cook double quantity of things, freezing half to make our own, low carb, ready meal for the following week.
Sally