1. The Anshei Mishmar may drink wine at night, but not during the day.
2. A Kohen who knows which day he is supposed to serve may not drink wine on that day, even nowadays.
3. There is a dispute about whether a Kohen with pure lineage may drink wine nowadays.
4. The Gemara discusses the mandatory haircut schedule for important Jewish figures.
5. Kohanim who serve in the Beis ha'Mikdash while they are drunk are liable to be killed by Heaven.
A BIT MORE
1. Even though it is not their day to serve in the Beis ha'Mikdash, since their family is serving they may be asked to help if there is are a lot of Korbanos that need to be offered that day. Since they might be needed to perform the service in the Beis ha'Mikdash, they may not drink wine.
2. Perhaps the Beis ha'Mikdash will be rebuilt and he will be called upon to serve.
3. The Tana Kama: He may not drink wine, as it is possible that he will be called upon to serve in the Beis ha'Mikdash when it is speedily rebuilt. Rebbi: While he understands the ruling of the Tana Kama, a Kohen may drink wine and we do not take into account the consideration that the Beis ha'Mikdash will be speedily rebuilt.
4. The king must take a haircut every day, and the Kohen Gadol must take a haircut every Erev Shabbos. A Kohen Hedyot must take a haircut once a month.
5. Any service that he performed under the influence of alcohol is invalid.