I use to be involved with a loose organization called Food Not Bombs in the USA. We used to go round to various grocery stores etc. and ask them to donate food, usually it would be food that was one day past its expiration date, meaning it is still good but could not be sold legally, so we said just give it to us rather than throw it away. This was all vegetarian food both because we promoted vegetarianism/veganism and because meat is unsafe past its expiration date (for that matter its often unsafe PRIOR to its expiration date). This was a good system cos there was no money involved hardly, we might have bought some bread or bagels to go along with it but basically it was something anyone could do, including homeless people themselves, without any money. We'd just cook up big feasts and give em away and we'd have propaganda (anti-war, anti-system etc) that people could take or leave as they wished, we didn't push it.
But be warned several people in the Bay Area were thrown in jail for doing this (for serving without a food handler's license, that kind of thing- really because the city gov't didn't want homeless people congregating in parks and 'scaring away the tourists' and so on.)
Good luck with the project.