You need to define the amount of cash and the circumstances. Under 10k, you can bring it on your person when entering the country. You can then proceed to sell it to a cueva. I don't think traveler's checks will do you much good because they will unable to be cashed at other than the "official rate". Bring unwrinkled USD hundreds with the blue ribbon and you'll get the proper exchange rate.
Edit: but you've been here a while. What's the question in that case? and the US bank to cash question doesn't relate if you are here, but i think it is 4k before they report it.