If I am involved in a traffic accident and when helping me the paramedics find an ounce of marijuana. Can this be used against me or is their a reasonable expecation of privacy?

No, they are assisting you in the course of their normal duties, not conducting a search. Besides , paramedics are not considered police agents so it can't be considered an unlawful search and seizure, just a citizen who stumbled onto an illegal substance.

The emergency doctrine trumps your privacy as you have no reasonable expectation of privacy when in an accident and you require care. You may want to get an attorney, but the hospital will inventory your goods and likely did a tox screen at police request, or as part of your treatment. Since it is likely it would have been discovered, the inevitable discovery doctrine may also apply to make the find non-excludable.