... the "sample size" bags that many quality dog food makers produce.
In the past I've had to special order boxes of "sampler bags" of dry dog food- which is expensive because it's not a regularly stocked item.
I try and carry a few bags in my truck at all times so I can give them to homeless people with dogs. This not only provides and often better balanced and more nutritious food then they will often otherwise be able to get, but in my experience most homeless with dogs will put their dogs needs first, so this takes a bit of burden off their human companion for at least a few days.
And yes, I've tried packaging up into ziplocks or even seal-a-meal bags from our large bag of food, but it is both time consuming and I think a little less effective (someone may well be wary of such food, but if it's in a sealed manufacturer package... )
Anyway- I think if a few more people were interested in this idea, it might bring the price down for all if the store could order larger quantities.
As a side note- I also tend to carry packages of cheap socks (an item homeless often are in dire need of because it is not an item of clothing generally put through the service networks)...and...well... cannabis.
Finally- I'd be interested in knowing of any veterinarians in the area who provide services for homeless people with pets, and who collect donations to help cover such services.