Can the police ticket me for something other than the purpose of the roadblock?

As long as the roadblock was conducted properly, the officer may look into the car when questioning the driver. If the officer sees contraband, such as an open container or a baggie of drugs, he may sieze them under the "plain view" doctrine: The officer is standing in a place where he has a right to be, that is, conducting a legal roadblock; and he may sieze contraband or evidence of a crime without first obtaining a warrant. 

Similarly, an officer who observes an infraction may issue a citation for that infraction.

by: Janet Portman, Attorney