How long can you keep alcohol before it goes bad?

If it's unopened, it can last for decades though beer is likely to not age well unless it's brewed specifically with that in mind.

Wine and hard liquor can typically last decades unopened and many wines taste better with age.

Once opened, beer quickly loses its carbonation, and wine will spoil within a few days if it's not refrigerated. If you keep it cool, it won't spoil but will start to taste blah after a week or so. You can keep it fresher longer by pulling the air out of it and sealing it.

Hard liquor lasts years even once opened.