Drunk in public is a crime that is often used as a catch all for the police. You are drunk in public if you are intoxicated by legal or illegal drugs that produce intoxication as well as the use of alcohol. There is no specific evidence that the police collect for this offense. Generally they do not perform breath tests or field sobriety tests as would be the case with DUI/DWI cases. Generally the smell of alcohol and/or any loss of bodily function or control however slight will be grounds for arrest. This charge is a class four misdemeanor which has a maximum penalty of a $250 fine. No jail time can be given for this offense, but you may be incarcerated during the time you are intoxicated.
Because of the minor nature of the charge most people do not retain counsel to defend this charge. However, some people do chose to retain counsel to fight this charge if they feel they are not guilty. This is technically a criminal conviction.
The main defense in these cases is to challenge the evidence at trial forcing the Officer to explain the specific observations that lead him to arrest you. Many times they will not be able to produce any evidence other than the smell of alcohol. Often Judges will not accept this as sufficient proof of guilt. You will have to evaluate the cost/benefit ratio in your circumstance to determine if you wish to retain counsel to defend this charge.