Ring of Sustenance

It might not be enough if he included the costs for food and drink, but Ainz was undead, while the ring on Narberal’s finger was imbued with magic that removed the need for her to eat or drink, which helped a lot in cutting costs.

- Overlord; Vol 2; Chapter 4

Hardly any of the monsters here needed to eat. In fact, Aura was also wearing a Ring of Sustenance, which eliminated the need for food or sleep. However, her master had insisted that “everyone must take breaks from time to time,” so she had to obey him despite her wishes.

- Overlord; Vol 4; Chapter 2

The maid bowed deeply as she expressed her gratitude.
“However, it is thanks to this item that you so graciously lent me that your servant could stay by your side to attend you without having to rest, Ainz-sama.”
No, that’s not what I meant, Ainz muttered in his heart.
It was true that once one put on a Ring of Sustenance, one could go all day and night without any sleep. Still, sitting on a chair and watching Ainz all night should have been nothing short of hellish. Although he was very pleased by their dedication, there was no need for them to go that far.
At least they should cancel the night shift… the part where they watch me sleep, right?

- Overlord; Vol 10; Chapter 1

Feeling a little depressed, Ainz handed Zenberu three items.
“Take them. This ring eliminates the need to sleep, eat or drink. This ring grants cold resistance. And this necklace grants the ability to use the [Fly] spell.

- Overlord; Vol 11; Chapter 2