Recently I came home after an unexpected stay in hospital, there was bread in the fridge. That had been good wholemeal bread before I left but after a week in the fridge it was so stale and hard that I couldn't have eaten it the way it was. I didn't think I was well enough to go out and buy bread or milk. I broke the bread into pieces, mixed it with rolled oats and some currants that I had in a store cupboard and some saccarin. I boiled up some water, added that to the dry ingredients above, stirred it and went away to rest while it was cooking. When it was cooked I went back, mixed some milk powder with a little cold water to make a paste and stirred that into the porridge/pudding. Because milk powder was added at the end I didn't have a milk mixture that could boil over and could safely rest outside the kitchen while it was cooking. I made it several times till the stale bread was used up, optionally I sometimes added some vegetable oil, they do not call it Canola in the UK but I think it is the same. When the currants were used up I made it without.
Recently I tried it with some almond essence that I had in the kitchen and I feel that improved it. I also tried it with fairly traded cocoa powder (if you cannot get that cocoa where you live other fairly traded cocoa also works)which was very good.
Result: It was edible, the currents became juicy through being boiled with water. It was neither specially tasty nor specially bad. It was easy on an invalid who did not want to stand too long in a kitchen and also easy to digest. I recommend this for invalids who find cooking or shopping tiring but must cater for themselves. If you are a healthy person cooking for an invalid please go to some trouble to buy tasty ingredients and stand in the kitchen as long as needed to make something good.
You can make porridge mixing wheat flour with rolled oats, this works with white flour or wholemeal flour. I've also made porridge mixing rye flour with rolled oats. Mix all the dry cereal ingredients together before adding any liquid. With white flour it still tastes like standard porridge made with oatmeal but has a finer, smoother texture. With wholemeal flour it tastes more like a wholemeal product. Porridge or gruel can also be made with wheat flour only, it needs milk, milk powder and/or sugar to make it taste acceptable. If you like porridge or milk pudding you may like to experiment with these different types of porridge when you are well. Porridge made with wheat flour or partly with wheat flour forms lumps even more easily than porridge made with rolled oats only so it's better to add cold water or cool water and stir it from time to time while it's coming to the boil. A blender can sort out any lumps but destroys the texture of rolled oats. You need to take a little extra care to avoid lumps if you haven't got a blender or if you like the texture of unblended rolled oats. If you are new to making porridge you need to stir the porridge frequently or all the time till you've added all the liquid you need and the porridge has stopped thickening.
If you are sick these suggestions may help you stretch whatever is in your kitchen till a friend can get you food or till you are well enough to go out shopping.
These traditional recipes could suit a healthy person cooking for an invalid. Most of the recipes were developed before people knew disadvantages from saturated fat in butter. Therefore substituting a modern spread with more unsaturated fat could be a good idea. There is also quite a bit of sugar in these recipes. I think sugar may be helpful for sick people of average weight who have not got much apetite and need energy to fight an infection. I am not a doctor and I am not sure about this. It may be possible to adapt these recipes to sweetners without sugar or to mix sweetners and sugar, I have not tried them.