This is a wiki, please add your own tips, general info, new restaurants and comments on already listed restaurants :)
Most shops close from 2 to 4:30 pm, except big stores or stores in touristic areas. They open around 10 am and close around 8:30 pm, except in touristic areas where they might close later. Most shops are closed on Sunday.
Restaurants usually open at 13:00, close at 16:00, and open again 20:00 till 24:00. Bars, and tapas bars, however, open continuously.
In Barcelona tips are minimal. Rounding to next euro amount in taxis and 0.5-1€ per person in restaurants is the norm.
Pick pocketing is supposed to be a problem in Barcelona. The area around the venue is generally safe, but it's a good idea not to bring anything of value that you don’t absolutely need. It doesn’t happen often, but it’s really annoying to get pick pocketed or mugged.
Some general tips when traveling as a foreigner in any large city, including Barcelona, are: keep your passports in your apartment; be careful when checking your smartphone on the streets and NEVER leave it on the table; carry handbags crossed around your shoulders; carry wallets inside zipped pockets (not in a back pocket, for example). While eating in restaurants, always have your bag either on your lap or tied up to the chair or with the strap around one of the chair/table legs. You may also want to remove your badge once you go outside the venue – no need to tell the world you're a tourist/foreigner.
In general, use your common sense and be aware of your surroundings :)
Buses are very slow, take subways if possible. You don´t need to buy the several-day metro/bus passes since you will be mostly walking to places close to the venue, which is quite centrally located. You will be better off just buying the T-10 (10 trip/10,2€ pay as you go ticket). Note T-10 is multi-person, i.e. more than one person can travel with the same ticked (obviously you still have to validate it as many times as people travelling). Only subway stations sell that ticket 10-trip ticket, which allows one transfer, bus- subway or vice versa. (it actually allows more than one transfer bus↔subway, but the rules are complex, to explain, so yes, let's settle on that). Also understand that “allows transfer” still means that you have to put the ticket on the machine, you can't just go into the bus without validating your ticket, the machine is just smart enough to not count it as a new trip when you're doing a proper transfer.
Buses do not take credit cards, only coins and small bills.
If you want to use a taxi, using an app like Free Now is very simple.
For lunch most restaurants offer some kind of set menu (what we call simply Menú or Menú del dia) which consists of a choice between some (usually around 4) starters, a choice between some main dishes, drink [and usually] dessert. This is less common for dinner. What in English is called “Menu” (i.e. choosing from the whole big list of things the restaurant does) is called “Carta” here.
Terra d’Escudella: Near Plaça Osca, 8 minutes from the venue. Fixed menu, nice traditional food.
Can Violí: Plaça Ibèria, 1 minute from the venue. They have a Menu of the Day.
Arturo: Carrer Sagunt, 104. baixos, 1 minute from the venue. This one is more expensive, like 30€ per person.
La Bricciola: C/Olzinelles,19, 1 minute from the venue. Italian Pizzeria
Can Coca: C/Jocs Florals 78-80, 1 minute from the venue. Simple fixed menu.
Flamant: C/ Enric Granados 23, really beautiful and not expensive (food is nice but simpler. Overall a winner). Better to make a reservation.
O'novo Chispa Good Galician restaurant, can get a bit pricy depending on what you order. 12 minutes away on foot from the venue
La Fonda: nice decor in central location, quite good food, very reasonably price, service might not be so good, it depends. You might have to wait, reservation is not possible.
El Casal: It´s not very big, but it a nice little place to try.
La Paradeta: Very low key and inexpensive, a bit noisy and unsophisticated decor, but good fish that you first go and choose (they charge by weight). It is cooked either grilled or fried and given to you in the order that is finished cooking. Expect to wait unless you arrive by 19:45.
Jai-Ca: crowded, unpretentious, not expensive and good.
Paellas are the typical Valencian food. Here are two options by the beach, it’s better if you reserve in advance. They are not cheap.
Can Majó: Foodies may prefer this one above Ca La Nuri.