Pebble of Sustenance
This is a small, smooth, round pebble of many vibrant and swirling colors. Swallow the pebble, and it sits in your stomach and nutritionally sustains you, obviating the need to eat. We’re talking complete nutrition. With just a pebble, you will have the healthiest diet possible. For about a month. But the pebble’s lifespan can be lengthened by supplementing it with food. Basically, if you eat, the pebble isn’t called upon to fulfill its purpose, but if you happen to go without food for some reason, it’ll be about a month before you start to starve. At which point, if you’ve got one, you can go ahead and take another pebble as if it were a Tylenol or whatever the fuck. And you can stop and start eating at any time. So a pebble acts as a stopgap measure when you can’t have food.
Only one pebble can be in your stomach at a time. If you swallow a new pebble before the old one is depleted, you’ll just hack the new one back up, somewhat uncomfortably. As long as you don’t accidentally lose it, a pebble can be coughed up multiple times and still be good when it eventually “takes”. Stop trying to swallow it too soon, yeah?
The pebble doesn’t quench thirst. So you’ll definitely die without water. You won’t be hungry, though.
The pebble slowly dissolves in your stomach, so the stone won’t pass through your system intact.
When you are carrying a pebble of sustenance in your stomach, your appetite is unaffected by the presence of the pebble. So it doesn’t feel weird to eat, even though the pebble is nutritionally sustaining you. It’s magic. It just works.