In terms of small items that are useful for the box, things to make more basic staples interesting would be good, so different spices or seasoning mixes to make the same basic meal different. Like beans done with Mexican seasoning and rice, or added into a Moroccan type stew, or made into a French cassoulet with a salami or chorizo sausage.....the same basic meal but you don't get totally fed up of it too fast.
I have a couple of the tiny and very highly concentrated squashes that Robinson's make, I bring them camping too, and come in a few different flavours, so help to keep drinking plenty of water. I also have some sachets of instant coffee, individually wrapped teabags, sticks of sugar (like those in coffee shops) and sachets of instant lemonade mix (latter from a transatlantic trip a while back) for camping and emergencies. But in my more general stores, I have a large box of my preferred teabags and 3 bags of ground coffee (knowing how much we're using when DH and I are both home!).
I don't have granulated sugar at home anyway as we use so little, I just buy castor instead - we use it in baking and it's just smaller ground for regular use. I buy that in 3kg bags, and have 1 in my stores. And a couple of 500g bags of brown sugar as I bake with that a fair bit.
Rice and pasta are regular staples anyway, but I also have other grains too. Long spaghetti, linguine and lasagna sheets. Arborio and pudding and sushi and basmati rice. Couscous and polenta. 1 long life pack of potato gnocchi. And a pack of panko bead crumbs. I should put a pack of instant mash in there too but we always have lots of both regular, baby and sweet potatoes that I can run through first.
Other than regular tins, the ones I have in my stash for more emergency situations are things like some bamboo shoots, clams, bean sprouts, corn etc - that I can use to pad out stir fry type ingredients (Chinese or Indian style mostly), and jars of sun dried tomatoes, peppers and olives to do more Italian/Mediterranean or Moroccan type padding of fresh stuff. I also have 1 bag of dried mushy peas for DH, and different types of tinned beans (4 bean mix, kidney, canellini, haricot, baked...) and pulses (chickpeas, lentils etc).
I've got 2 tins of evaporated milk and 2 of condensed milk (1 for baking the other for adding water and drinking), and some oat milk as a long life option. Which has surprisingly become a weekly shopping item in this lockdown! (I only opened it to try, DH and dd both loved it! And they drink pints and pints each week between them, so having oat in coffee/porridge and cows in tea and plain glasses is working well).
I also have treats in my tub in the wardrobe, and spare liquid soap for hand washing as that was very hard to get. Some cans of coke, lots of cans of tonic. A couple of specific toiletries that we've found hard to get, to have a spare (other than the "next one to open" in the bathroom cupboard). Batteries for torches and radios. A deck of cards, notebook and pen. I have meds in a different place, but enough general pain, upset stomach and gut, hay fever and muscle strain relief as well as general first aid supplies in there. Not enough gloves, but will restock those soon.
Prepping for Covid and lockdown at home when general services are functioning ok is different to thinking about storms or other natural disasters, and the preparation you might need to do for those. I am starting to think about potential water issues this summer. So think carefully about the "why am I prepping?" before starting the buying and filling, to know what best to buy.