Top 10 Excuses for Leaving Work Early
Those darn delivery companies seem to only be able to deliver things during working hours. Your working hours, that is.
It won't fly more then once a month or so, but it's totally plausible that you ordered some new furniture and the delivery company can only bring it over during working hours.
Hopefully you haven't told your boss yet that you're still living with your parents.
Personal issues are wonderful because, well, they're personal. If your boss is particularly inquisitive, tell him/her it's personal and family related.
If you don't use this excuse more then, say, once - ever - then it should be alright.