Grew up in Emerald Isle.
Traffic:
Traffic over the bridge can back up, particularly on weekends around the times when people are able to check into their cottages. If you're hitting the island early enough to get lunch, you should be okay...traffic hasn't been as bad in the last couple of years because NCDOT widened the road leading to the bridge (tip: the right lane merges into the left lane right past the tourism board), tourism has been down due to the economy, and Emerald Isle Realty got their shit together and stopped backing traffic up onto the main road. Looks like traffic has been picking up a bit this year, though.
If you get stuck in traffic, just stay on the main road until you hit Islander Drive (1st Bert's on left; putt-putt with fake Lookout Light on right); take right on Islander then a left on Reed. Stay on Reed all the way to Mangrove; take a left on Mangrove (Bluewater Associates is at that corner) and go through the stop light. Take a left past the car wash, and follow that road around the curve until you hit the marina; continue right at the marina down Sound Drive. You can go down Sound Drive until you hit Lee; take a right on Lee. Go down Lee until you hit Canal (after Archer's Creek and before the main road); take a left on Canal. Go down Canal until you hit Craig; take right on Craig and you'll be back up at the main road, past the commercial "district." The real estate companies aren't that far down, though--if you need to pick up your keys, you'll want to come back up on either Bogue Inlet or Cedar.
Restaurants:
I second Big Oak, and I'd stay far, far away from Bushwackers. Note: Big Oak is a drive-in with outdoor seating, so if you're looking for a sit down that won't help you much.
Most people have a love/hate relationship with the rest of the restaurants in EI...Rucker John's is in Emerald Plantation and is a decent stand-by; if you're looking for fried seafood with a pretty low-key environment, try Jordan's. I can't speak much to the restaurants down towards Salter Path; we're closer to the police station. I've heard that Circle Pizza is good, but pricey. Flipper'z (in the K&V Plaza; turn off at the CVS) is okay...nothing outstanding. There's also an Andy's and a pizza place (Michaelangelo's) in the Plantation, as well.
Kathryn's is supposed to be pretty good--it's run by a guy I went to HS with--but I don't think they're open for lunch. His family also owns Portofino's.
Hit up Willis' if you're looking for fresh seafood to cook at home while you're there.
TL;DR-
Seriously, just go to Big Oak and grab some shrimp burgers.