Options close to Zilker Park?
Eating ACL is though as most of the places nearby are packed. The food inside the festival while only fair and not cheap is at least diverse more than your typical burgers and hot dogs. You can usually find things like hummus, deer sausage, asian style noodles, etc.
P. Terry's is a locally owned burger place with a so-so burger but good fries and a good veggie burger and chicken burger and is about a 10 minute walk from festival grounds.
I agree with the other post that Uchi is a great option but you'll have to clean up beforehand and as they don't take reservations after 7pm you may well be starving by the time you get your food.
If you just go for the festival and look forward to a good pre-show brunch, Lambert's is my top choice downtown. $22 for all you can eat breakfast food items and if you hit the right time, some of the best 'cue in the city limits.
P Terry's Burger Stand
404 S Lamar Blvd, Austin, TX 78704
Lamberts Downtown Barbeque
401 West 2nd Street, Austin, TX 78701
Twill's suggestion of Flip Happy is a great one. Other than that most of the places in the immediate area are best left for a margarita and sunshine.
Starting a food file is a good idea. I love this website, but please don't rely on the guide to ACL dining found on Chowhound. It certainly does not guide you to the best places in Austin.
re: Honey Bee
Off the top of my head here are some suggestions that are within a 15 minute drive of Zilker:
Whole Foods on 6th will be crowded, but a good place to restock on fruit, water, and snacks.
Polvo's on South First- Not as good as most seedy taquerias, but better than most Tex-Mex available in other cities. I like their fajitas.
Angie's on East 7th- I can only attest to their carnitas tacos (that is all I ever order), but they are very good.
Sam's BBQ- Roll to the East Side and visit the sassy sisters who dish out BBQ until 2 am.
Vespaio and/or Enotecca- sister restaurants on South Congress; best Italian food in Austin (IMHO)
House Park BBQ- Lamar and 12th. Only open for lunch.
Enjoy our great city.
People will likely guide you to certain "Austin Institutions" such as Magnolia, Kerbey Lane, Chuy's, Shady Grove, Hula Hut. All of these places can be fun, but the food is nothing special and ranges from bland to okay. They will all be packed during ACL.
re: Honey Bee
I think that your biggest obstacle is going to be getting to experience outstanding Austin fare within the restrictions posed by the festival. Obviously, if you're willing to leave the park a bit early (and don't have a problem with dining dirty), you'll have a better chance to try certain restaurants that don't have extended hours aided in no small way by the moderated traffic congestion.
There are a few on the board that would agree with my contention that Uchi is one of, if not the best dining experience in Austin, and it would be easy to get there from Zilker...but only if you're willing to skip what will inevitably be the biggest draws of ACL in the form of the evening shows.
If your primary goal is to take in as much music, sun, people watching, beer and dirt as you can in your short stay, then you may want to focus on late night/24-hour dining or breakfast/brunch spots.
A couple of blocks off Barton Springs within spitting distance of Zilker is Flip Happy Crepes ( http://fliphappycrepes.com/ ), one of the ubiquitous Austin trailers with that distinctly Austin flair. For a primer, check your local listings for "Throwdown" on the Food Network as they will be featured in early August. I don't know if they'll be extending hours during ACL, so you may have to catch them on the way in, but it'll be well worth it.
Flip Happy Crepes
400 Jessie St, Austin, TX 78704
Made me laugh. I am going to assume by "foodie" you mean people that want to eat something actually good and not pay a crazy price for it. If you are looking for more fine dining, there are lots of posts about that.
Sounds like you want better food than what is right by Zilker park. (God bless those Barton Springs restaurants, but great food is not what they are serving. Not that there is anything wrong with good ambience or convenience.) Besides they will be full of folk who don't know better or just want to eat.
Taco Deli would be a long walk from Zilker, but not unreasonable – they have good tacos. (I like the fish and the mojo tacos. But there are lots of other options) They have been up and down, but they have good, fresh food. I wonder if there would be a bus that could take you closer? They are on Spyglass. No dinner.
There is also Phoenicia on Lamar. More likely bus route. Good kafta, sandwiches, zatar. Also no dinner, no tables. Maybe Curras on Oltorf is also on the bus route? Sandy's has a decent hamburger and good enough frozen custard. No dining room, only picnic tables outside.
Of course, there will be shuttles downtown, and there are a whole lot of options that way. You could walk to Whole Foods (it is not a short walk, but also not unreasonable), which would make sense when you don't need a waiter and can't decide what you want.
If you are not from Austin, I can be more helpful with directions.