bar is all about the alcohol. People come here to drink and then drink some more. As such, food at a bar essentially centers around appetizers or snacks; something to make the alcohol taste better. A pub, on the other hand, is like a restaurant that serves great alcoholic drinks too.
A dive bar is typically a small, unglamorous, eclectic, old-style bar with inexpensive drinks and may feature dim lighting, shabby or dated decor, neon beer signs, packaged beer sales, cash-only service, and a local clientele.