I used to live down the street from the Barclays Center and let me tell you there's all kinds of great food options in the area. Barclays sits on the end of Park Slope's 5th Avenue and 5th Ave has everything you can poke a stick at. The closest place though is Shake Shack, literally across the road from Barclays on Flatbush Ave there's Shake Shack for quick delicious freshly made burgers. Back to 5th Ave there's Donut deli's - Area Bagels is my favorite for local NY style lox and creamcheese. Next there's a number of low priced 'hole-in-the-wall' Chinese takeaways. Lot's of Mexican restaurants, Thai, Japanese, even Indian. Keep venturing up 5th Ave and you'll find an abundance of choice.