There's no standard there. Big companies tend to wipe the disk and reinstall everything, but as always, it depends. Reinstalling everything is a lot of effort, and especially development environments take a lot of time to establish.
Even if there's some policy, you should always suspect that wiping hard disks after previous workers may not be considered crucial, and in end effect, the new employee may gain access to all data you have stored on the hard disk.
Personally, I recommend cleaning up. You don't want someone else to use your Google Account or anything similar. Generally, if application data is encrypted, they should be safe (read: useless for anybody else using the same computer), but you should clean them anyway. Someone could have the idea to require from you to change your password to some standard one just before leaving, which would compromise the protection given by the encryption.
As for job-related stuff like SQL queries, if you have good relations with your still-current employer, it would be a good idea to keep them, because they may be useful after you leave, and it would be nice to inform them where are they stored and what are they doing.