Kliss is one of the Noble ladies that attend the balls that vin also goes to. She turns out to be an informant, and requests payment from Vin when she reveals a secret.
"Wait!" Vin said. "What was that you said about Elend earlier? He's going to get what he deserves?"
"Hum?" Kliss said, turning. "Why . . . that's right. You've been asking after Shan Elariel's plans, haven't you?"
Shan? Vin thought with rising concern. "What is she planning?"
"Now that, my dear, is an expensive secret indeed. I could tell you . . . but then, what would I have in return? A woman of an unimportant house like myself needs to find sustenance somewhere. . . ."
Now at this point I assumed she could have meant anything sustaining, and the usage is quite broad. However it's emphasised again a little later
Vin turned back to the smiling Kliss. The woman winked at her. "I'll keep your Allomancy a secret, child. Just make certain I get payment by tomorrow afternoon. A lady must buy food—and as you can see, I need a lot of it.
'I need a lot of it' seems like such an odd turn of phrase. I had gotten the impression, previously, that Kliss was a short, plump woman from this:
Kliss turned eagerly, obviously excited by the prospect of another person with whom to gossip. “Lady Valette!” she said, waddling forward
So not someone natural needing 'a lot' of food.
I know it seems like such a small point to pick up on, but it really caught me as a strange thing to emphasise by mentioning twice.
The only thing I could find was a quote from the author:
Kliss was intended to be a throw-away character used in one chapter, but now she's become an informant and a conspirator.
So, why did Kliss need so much food? Surely there's plenty at the ball, and also back at her houses' 'keep'? Even the unimportant houses would be wealthy enough to feed their nobles excessively well?