Whole host of decent eateries in the Northern Quarter, maybe 5 minutes walk or so from the venue. Check out Thomas Street for a range of options. For pre event food I'd recommend Dough. It's on the junction of Thomas St and the High St and is a very original pizza joint ( a one-off as well, not a chain). Proper wood fired oven and nice crispy bases (you choose what type of base you want) and whilst you'll get a lot of the "usual suspect" pizzas, there are loads of toppings and combos that will surprise and delight!
Alternatively, just up from Dough you've got the Northern Quarter restaurant and the Market restaurant. Both more expensive, both original in their own way. More gourmet grub, but probably a bit slower, more a destination in their own right than a place to go to before moving on, if that makes sense.
Anyway, there are loads of good eateries and bars in that area if pizza ain't your thang, get there as early as you can and have a good nose around, you won't be disappointed