Hope you are feeling better now and getting plenty of rest to help you recover. It's really tough being ill with no-one to call on and trying to cope with everything else on top. I've managed for years on my own, including a couple of occassions as you describe.
People think you are strong and managing, because you have no choice but to get on with it. I stopped asking for help from my family because it hurt when none was forthcoming and it just got me down and more depressed that they weren't there for me or ds. One of the other mum;s at ds's primary school once told me that she actually felt intimidated by me because I was able to do it on my own, yet she struggled with the help of her husband and parents and also didn't work. To her it looked like I was able to do it all. Yet it really didn't feel to me like I was managing/coping at the time. The difference was I just had to get on with it because there was no other choice but to sink or swim.
I remember a severe bout of flu, like you describe, when I found myself crawling downstairs on my hands and knees to put a pizza in the oven for ds and barely being able to get back upstairs after. After that I told him to help himself to cereal and crisps for a couple of days! And another occassion when I had my arm in a sling and couldn't drive, was signed off work, and even cooking was a struggle but still no-one offered any help with ds or shopping etc. It's only now I have cancer and am going through chemo that people (my family and others) are coming out of the woodwork and offering to actually help me and making the effort to text, call, and visit me...
What I'm trying to say is that if you can't manage to cook then the dc will survive a couple of days on biscuits, crips and/or cereal. Assuming you have any of those in your cupboards....
I use Ocado (its range of vegi foods is far superior to anywhere else). They also rarely have substitutions, so I know I will almost always get what I've ordered except very occassionally around the holidays. Their drivers are really kind and helpful too and don't bat an eyelid at my chaotic mess of a house or when I answer the door in my dressing gown and haven't put a hat on to hide my bald head. They offered 1 hour slots ages before the others jumped on that band wagon too and always phone if they are going to be early or late (usually they come a bit early ime).
If you book it early enough you can usually get it delivered the next day. I have an ocado midweek delivery pass though, so get more choice of slots and only have to spend 40 per shop. I also get a lower delivery price if I want it outside the midweek times. Highly recommend them, whether you are ill or not!