Barcelona's such a fun city. If you're into parties, the "Arena" clubs on weekends are great. They run like 5 different clubs under that general brand. We enjoyed the "Arena VIP" one the most.
In terms of food, I don't remember any restaurants in particular. It depends on your budget (BCN can be expensive sometimes). You can get inexpensive fruit platters and snacks at the market right off La Ramblas. I believe it's this one:
Mercat de Sant Josep/ La Boqueria
La Rambla de Sant Josep
Metro: Liceu, (Green Line, L3)
Mon-Sat: 08:00 - 20:30http://www.barcelona-tourist-guide.com/en/shopping/barcelona-market.html
Beyond the typical Gaudi sites (which are cool), a nice place to visit is the Picasso museum, featuring his early works. I never appreciated his art until we went there. It shows the whole process and how he developed his unique style. A real eye-opener.
One thing to keep in mind is the 100ml rule when travelling to Europe. I've seen quite a few people have perfumes, colognes, booze etc. confiscated by airport security. In BCN your bags get scanned also upon arrival (strangely), so it's even more of a problem. It pays to make sure anything with more than 100ml of liquid is packed in your checked luggage, to avoid problems.