There's lots of late bars in town, some staying open as late as 400 - 6.00 AM.
If you just want a late drink and nothing else, from where you are, The Grapes on Mathew street is open till about 4.30 AM on a weekend.
Just a bog standard pub, it's a little bit small and cramped, as it's always busy. Smokers yard out back. Usaually decent music on, that carries a tune to sing along to.
Rubber soul is another open till 4.00 AM.......... In fact, there's a number of later openings around that area.