Purple it's about getting little and often.
The things I've collected are all cheap.
dried beans, tinned tomatoes/passata.
Buy an extra thing a week every week and it will build up.
I realise that's still money that you don't have- but if you possibly can manage something, it will help.
The bigger issue for less well off people, IMO, is storage space. I have a garage and a bigger than usual house. I have places to keep my stash. Many people don't.