you keep mentioning disposable income, as tho that's a measure that determines buying power. It's not. The measure is available funds, regardless of source.
A person with a lot of available funds _do_ have a higher claim than someone who doesn't. The source of the funds may be their prior work and savings (aka, disposable funds), or it could be funds collected from many people (such as donations, or family pooling funds). It is not clear how you can make a distinction between many people pooling their funds, vs somebody who has collected large amount of funds prior (from income or wealth). This is why price fixing doesn't work well, except under quite exceptional circumstances (e.g., all transport infrastructure is disrupted), in which case, rationing by decree works better than price fixing.
But even if shopping on behalf of the entire neighborhood is common, is protecting that strategy more important than deterring hoarders and preserving the ability of underprivileged people to buy what they need for themselves?
The assumption that everyone has the same need is less wrong than a system that implicitly assumes need is proportional to disposable income. Someone walking into a retail store to buy on behalf of six dozen people is theoretically possible, but definitely is not common, and almost certainly less common than someone trying to hoard excess supplies for personal use.