Something old, beat to hell, domestic to your region, running, but probably had minor issues.
-Learn something about fixing car problems (domestic means cheaper parts)
-It's bound to be slow, so you will wind up in less trouble
-It's a hunk of shit, so when you inevitably end up in an accident (your fault or just the nature of a school parking lot) it's not as big of a deal
-When you finally buy your own car you'll appreciate it 1000X more