If you notice any concerning behaviour or damage, report this to the appropriate authority as soon as you can. This might be the Department of Conservation (there may be a ranger on duty), or the local/regional councils. Make sure you advise them of how alcohol has contributed to the problem.
Any serious issues affecting the safey of yourself and/or others should be reported to the Police or other emergency services.
For more information, please check out the sub-section on Alcohol in public places