I found the awkward sentence when translating it into Korean.
It is "I could use an escape to tropics."
My book said it means (translated into English)
"I want to escape to tropics." or "I need an escape(vacation) to tropics."
Basically, I think "could" means "capability or (not that convincing) guess" and "use" means "do something with it".
Therefore, the sentence like "You could use that cup" makes sense.
But, why does the "necessity" meaning emerge?