(Sorry, I meant to get this up before Opening Day like I did last year, but it didn't happen.)
Everyone knows you can carry in food at the stadium, right? Why anyone buys food at the park is beyond me. Here are my recommendations for local eateries, as a long-time Hill resident. If you're driving in, these are all easy pit stops on the way. If you're taking the Metro, you can get out at Eastern Market or Capitol South, and then grab the Union Station-Navy Yard Circulator bus, which runs past all these places every 10 minutes and takes you right to the stadium for a buck.
La Plaza (Mexican and Salvadorean)
629 Pennsylvania Ave SE
Fantastic margaritas, yummy bottomless chips and salsa, and the best damn service you'll get anywhere. The place is run by a great guy named Henry Mendoza, and pretty much everyone I know who's gone there became a regular. You have a lot of choices for Mexican on the Hill, but forget Banana Cafe, Las Placitas, or La Lomita. La Plaza es el mejor.
653 Pennsylvania Ave. SE
Great Thai place. I always get the panang curry or pad see ew tofu, which can all be served with chicken, beef, pork, tofu or seafood, and the blanket shrimp appetizer is perfect picnic type food.
Cava (Mediterranean tapas)
527 8th Street SE
This place is absolutely delicious. Great addition to the Hill restaurants. Cold tapas is a good carry out option, though it may be better as a snack than a meal. Like La Plaza, this is worth leaving extra time and eating before or after the game on the weekend.
Good Stuff Eatery (burgers)
303 Pennsylvania Ave S.E.
There's a Five Guys right by the park, but for my money Good Stuff beats Five Guys with a stick all day long. The owner is a guy named Spike who went on one of those TV cooking reality shows on cable. All the burgers are great, and I recommend also getting the onion rings and a milkshake (don't forget to finish the shake before you get to the park--you can't carry in drinks).
Capitol Hill Tandoor & Grill (Indian)
419 8th Street SE
Good, reasonably priced Indian food, easy to carry out and eat in the bowls they give you. They aren't super-slow or anything, but it's a good idea to call 10-15 minutes ahead if you're in a rush. I recommend the malai kofta and paneer makhni entrees, and don't forget the kashmiri naan and vegetable pakora appetizer.
Starfish Cafe (seafood)
539 8th Street, SE
This is more of a sit-down place, but you won't be sorry carrying out a po' boy. They come in shrimp, catfish, oysters, and scallops varieties. This isn't really a budget option, but you'll get your money's worth. Also if you have a minute I recommend a mojito at the bar.