
I have left out the photosharing apps here like facebook, instagram, picplz, tumblr, and I have also left out the best reference, the Sched.org mobile website where I have picked out a panel and party agenda (official parties only) and plancast but these posterity pic-ers and schedule gatherers are not the focus of SXSWi for me. For me, the fun is in the hunt. The hunt that I'm talking about is the hunt for the best of everything in Austin, and these apps are most likely how I will find them. More accurately these apps will help me cheat off of those SXSW A-listers who have arrived before I have.
The 2011 SXSWi apps:
bump, hashable, yobongo, foodspotting, beluga, groupme, ditto!, LoKast, rdio, foursquare, twitter and HeyTell are going to be my signals. Will I be as excited about them on 3/15 as I am now? Definitely not, hence the precarious 'x's. Why have I chosen these above all others? If you are wondering why constrain myself at all, you're right Fred Wilson had a great post about mobile notifications on 3/1 which shows Android's superior notifications architecture for letting you have more and more engagement apps on without relying on them all to be on your home screen. But with 144 apps on my phone post cleanup this week (I had 6.6 gb of apps, was getting close to my limit on 16gb iPhone 4), I felt it was time to focus on what could fit in a folder (12), and since on top of that there's a tremendous amount of overlap in this group, here is my reasoning for why each of them gets a spot in the SXSWi folder. (for the record I hate iOS folders :) )
bump, intros, sharing contacts, sharing apps, sharing music, chat with contacts
hashable, intros
yobongo, meeting new people when chatting about panels / parties, deciding on things
foodspotting, figuring out the best bbq!
beluga, chatting with housemates, prepping with panel participants
groupme, finding friends, chatting, sharing links / photos to make people laugh
ditto!, deciding on things, crowdsourcing plans for the day / evening, pushing serrendipity
LoKast, sharing songs, photos with people nearby
rdio, searching for and downloading music, checking out what friends at SXSW are listening to
foursquare, finding out what's next, being findable, posting photos, finding addresses
twitter commenting on everything, seeing what's trending, sharing with people back home
HeyTell chatting with housemates like I'm on a Sprint Nextell / Boost phone or walkie talkie!

Those 12 Angry Apps are not the whole story. There are a class of apps that are invisible, they are API services that are plugging into one of those above apps, most likely Foursquare or Twitter.
These aftermarket, app-boosting services are going to be providing more than their share of the fun at SXSWi. These are clearly extra credit apps, but if you have time to set these up you might be surprised at how funny make your social experience:
Tweetgrabber, a friend, Matt Newberg who I met at SXSWi last year just launched this ingenious service which helps you follow specifically someone's Favorites on Twitter and lets you store them in your unread Instapaper. This is a wormhole into the psyche of those you'd like to follow on twitter, so much more revealing than reading what they choose to tell you on Twitter.
Assisted Serendipity, another brilliantly devised and simple service that hooks into Foursquare and emails you based on the 10 venues that you think will most likely have desirables of the opposite sex in attendance. The way to set up this service is you put the number of the Foursquare number (which comes after the 'venue/' in the 4sq URL) and set the female : male ratio (or vice versa) to your liking and wait for assisted serendity to send you an email with those profiles so you can decide whether or not to go.
Don't Eat.at This service as the picture shows can be hilarious if mixed with other food apps like foodspotting. Basically, if you are going to use this app, make sure that you check-in before you foodspot! However, I mentioned this only because it was funny, in truth, this is currently a NYC only app, so I guess donteat.at won't spoil your fun in Austin!
For those of you who have not been to SXSW interactive before, then here's my advice for gearing up.

This is a picture of my pre-SXSW stockup. I'm going to be staying up by UT Austin at a house that we've named HxSW II, casa chalupa, so I have rented a bike, and am bringing the New York Lock by Kryptonite with a deterrent that goes to '11'. I'm also bringing a Mophie Juice Pack: Boost which is the largest charger available that plugs into the bottom of an iPhone. It gives ~1 full charge but is still pretty discreet even when attached to the phone in your front pocket and has a carabiner for carrying on a belt loop / back pocket when you're not using it.
Also, on my trip to Barcelona for Mobile World Congress I bought a Monster Power Outlets to Go 3 with USB. For times when you have plugs near you (like near the stage at Stubbs!) this small outlet strip will come in handy to power up more than 1 device at a time. Actually, I had even grander power plans but waited too long to get one of these solar panels from Voltaic for my backpack.
I agree with Fashism's post that bringing regular running sneakers are not necessary at SXSW, but, I would disagree about bringing sneakers in general. There's a ton of walking going on at SXSWi and the daily fashion show that I've seen for the past 3 years has been about cool t-shirts and kicks, so remember to bring yours! Also, although it's pretty dry in Texas, many of the best events day or night have an outdoor component to them, like an outdoor courtyard (remember the rainy 4sq party last year?) or roofdeck so there's a very good chance you'll get caught in the rain at some point. Try to stash a rain jacket somewhere on you when rain threatens.
Remember to come and see Check-in 2 Check-out: Mobile Audience Engagement in 2011 on Tuesday 3/15 at 9:30 at the Hyatt! Let us... @jakemintz, @foolazy, @ladylexy, @BB_iojbegun and @tomlimongello ...know when you've checked in on Sitby.us
and now for the uberlink with all the links from this post and beyond that might be useful to you in Austin.