Sounds like dumpster diving would be an easier approach

Not in any city I have lived in, AFAICT. Where I am now, the dumpsters are kept out of sight. When dumpsters are in sight, they tend to be in cages, as they worry about liability of unsafe consumption. Maybe i'm not scoping it out well enough but it looks like shoplifting would be easier.

(edit) though I should mention there is some kind of program where students can cheaply subscribe to receive food that is either expired or nearly so. I don’t know the details but that would be the easiest option (for students).

Also in many places its legal to sell expired food, its just not common practice.

I think I recall asking a cashier to lower the price on something that expired (they will usually do that on the last valid day), and they said /no/ we cannot sell that, and took it from me. So apparently it's illegal where i am.