From Faces of the Forgotten North -
Blanket of Sustenance: This finely-woven blanket can be worn as a cloak by a humanoid creature, but is more commonly used as a saddle blanket for a steed. Once per day, it provides the benefits of the sustenance power, allowing the creature to go without food and water for the day. Faint psychometabolism; ML 3rd, Craft Universal Item, sustenance; Price 12,000 Cp.
It stands to reason that in Dark Sun a sustenance item would cost more than a ring of sustenance in a standard D&D setting. There is a slight error in description - this is a continual use item, not a once a day item. A once a day item would be 2400 cp. That would be breaking the spirit of the item design, however, because the sustenance power lasts for a day anyway.
While having a blanket item of this type is no problem, it makes more sense as a body slot item. I can imagine that merchant houses will invest in a collar of sustenance for their mekillots, who are carnivores and not cheap or easy to feed on the roads.