I spent more than a decade on benefits as a single parent carer to a disabled child. We really had to scrimp at times, especially the early days before I'd worked out how the benefits system worked and learned that I could get DLA. Looking back, we always had enough food to eat but it was fairly basic food, and often cheaper ready made stuff as that's the kind of thing that was easiest to prepare. Sometimes I couldn't manage to make sandwiches for a day out, so I'd have to buy them, but I'd just buy one sandwich for us both, and I'd eat his crusts as he wouldn't eat them. And I'd chew my food slowly so I wouldn't have to fork out for a drink to wash it down.
He's an adult now and we are far more comfortable financially. We still make our own sandwiches for days out, bringing our own water bottles and claiming every discount we can (free carer entry and free travelcard). I'm a bit more relaxed with food shopping, as I can see that it's better in the long run to buy healthy food, and use more premium brands if the quality is better, but I bulk out meals and batch cook as much as possible.
There are some things that I baulk at doing, even though it wouldn't make too much of a dent in our finances. Running a car (as we get free travel/disabled railcard), using taxis, getting a pet, paying for haircuts or manicures, buying takeaway coffees, I repair clothes, use old clothes as wash rags, load up the freezer with yellow sticker bargains, resist putting the heating on for as long as we can, buy clothes a little too big for my toddler and hem the legs/sleeves to maximise the time she can wear them. And I sanitise my hands using public sanitiser points as much as I can, to avoid running down my own supplies!