If you're trying to make a good impression with the boss, don't be the last to leave. Sure, the free food and drinks might be a tempting reason to stay and enjoy, but your employer is likely to notice if you haven't left the bar and don't seem likely to leave anytime soon. This is definitely bound to create a lasting impression, just probably not the one you were hoping to make. Instead, come on time and make the most of your visit. Mingle with your co-workers and find time to chat with the boss for a bit, but once people start filing out, take the hint and get going with the rest of them. You don't want to be the first to leave, but lingering too late is just as bad.