Recently I realised that a solar-powered garden light could easily hide an ESP32 and has its own power source. You could even place them in public without being too suspicious. Might want to disable the light, so the power lasts longer and so it's less likely to annoy someone into removing it.

Someone can do the math on panel and battery size. I'm thinking it'll work as-is, as the ESP with WiFi on will draw similar power to the LED that you disconnected.

But how will you give it even a GB of storage for a tiny model?