To answer your initial question, a petit theft 2nd degree means it is punishable by up to 60 days jail. It sounds as if he may have already served enough time for that. However, you also indicated there was a drug charge. Without knowing more information since there are many different types and degrees of drug charges, it's impossible to tell you what his punishment will be. You need to get your son an attorney right away.
Petit theft can be charged as a first or second degree misdemeanor depending on the circumstances and the value of the property stolen. It can also be charged as a felony if the defendant is a repeat offender for the same crime. If charged as a second degree misdemeanor, the maximum possible sentence is 60 days in jail or 6 months of probation. If charged as a first degree misdemeanor, the maximum sentence is 1 year in jail. If charged as a felony, the maximum sentence is 5 years in prison.
Determining what your son's punishment will be really depends on the judge, the prosecutor, his defense attorney, his exact history, and the specific facts of his case. No one can tell you for sure what his punishment will be. If he is charged with a second degree misdemeanor, the punishment should not be too severe, but his criminal history could greatly impact the ultimate disposition of his case.