Check the civpedia (Help button, upper right on the main screen). Click on the resources tab. It lists luxuries, food, and strategic resources & tells you what improvements you need to work them. Generally, food tiles - fish, cows, sheep, wheat, bananas, deer - are not luxuries, but give your city bonus food, production, or gold. So they're worth developing but don't add happiness. Likewise, strategic resources - horses, iron, coal, etc. - don't add happiness but are crucial for building certain units or buildings. They don't get revealed on the map until you research the appropriate tech, though.