A Ring of Sustenance would be my death. I enjoy eating, which means I'd keep doing it, and if the Ring is providing all of my nutritional needs, that just means that everything I shove in my gob would turn straight to fat...
Always figured that the ring would compensate, the same way it provides optimal nutritional value for the wearer regardless of whether he's a librarian or a barbarian.
Even better would be if the ring were enchanted with both
sustenance and
regeneration. You may not think that
regeneration is useful for someone who doesn't get his limbs mangled on a regular basis... but muscle fatigue is a form of injury. For that matter, so are the cognitive deficiencies caused by a lack of sleep. Rapid healing combined with the optimal nutritional intake from the ring of
sustenance...
If that doesn't count as "cheating", that's what I'd want.
An obvious one that would have immense use for a "real world" commoner would be a
Decanter_of_Endless_Water. Imagine the usefulness for villages in arid regions, or for a farmer during a drought (just to name a couple).
Not to mention, perpetual motion. At the very least, you could hook it up to a turbine and power your bottling plant-- if not provide electrical power for the surrounding region. (Need someone smart to figure the actual numbers for me, unfortunately.) Keep it a secret so you don't bottom out the market-- or get yourself assassinated-- and you could probably make enough money in a couple decades to take your decanter to Mars.
Second choice. I think I'd still take the plain
ring of sustenance over this, but it'd be a close call.
Of course, what I'd really want is a full set of
tomes and
manuals +5. I'd settle for a
belt of magnificence.