I've been a single mum most of dds life and had a couple times I was extremely unwell and had to find workarounds.
Sensible to plan, but chances are you wouldn't both be equally unwell at exactly the same time.
As several pps convenience food isn't going to kill them for a short spell (or even medium to be honest)
That said there are healthier things that require little to no prep and are easy to eat, for perishables bear in mind keeping on top of use by dates etc.
Ready prepped veg that can be eaten raw:
Carrot sticks, cherry tomatoes, peppers, salad leaves, cucumber, celery, mange tout, baby corn, broccoli (yes really)
Fruit of course - we tend to favour fresh but remember dried and tinned fruit contains good nutrition too - just alongside a lot of sugar! Sainsburys do very child friendly dried fruit snack packs and also sell the whitworths ones - there's a little notch to make it easier to open. I love the apricots best but there's also usual raisins plus pineapple, pear, raisin and craisin mix.
Milk is also good nutritionally, your youngest I suspect still has a lot of milk but has your eldest veered away? If so might be good to get them to love it again. Yogurts are good too and of course very easy to eat.
Fruit juice and smoothies - again not ideal choices normally as a regular thing due to the high sugar but in a pinch they do also contain nutrients AND could help mitigate the erm...clogging effects? of an otherwise less healthy diet at such a time.
In terms of organisation I'd maybe look at the older ones time telling skills as a foundation? Little ones can find it tricky.