but I see it like trying to fill a jug with a hole in the bottom.

If viewed from the perspective that the community fridge isn’t solving the issue of the people near it needing it to be continuously resupplied, then yes, it is a ‘bottomless pit’. But at the same time, what it is providing is a somewhat constant relief from the system which created the circumstances for a community fridge to be needed, which means its also a source of endless/ongoing harm reduction.

But, if the community fridge is viewed as one tool in our belt with which to build alternative systems that would eventually allow us to decouple from our current one, then it is not a bottomless pit, and instead is one very needed and useful stepping stone leading to a much more egalitarian and prosperous society that could eliminate food deserts and wage labor entirely. In that way, a community fridge is just one form of prefiguration. Specifically, a community fridge is building out one part of a gift-economy.

If you’d like to see the end result of those efforts visualized in a very realisistic manner, I’d highly suggest The Dispossessed by Ursula LeGuin, which is a classic sci-fi novel based in an egalitarian gift-economy, and goes quite in-depth on how it functions.