I'm in transit as I write this on the way to Dreamforce 2012. I've got my iPad fully loaded to be a mobile office (though I've got my laptop along for the ride as well). To make the most of the trip, I've got a grab bag of apps that I recommend for anyone doing this sort of conference. I've left out obvious choices, like a web browser, email client, calendar, and social media apps because those are practically common sense at this point.
Fing: This is an iPhone/iPad app that scans WiFi signals nearby and lets you know which networks are open and have the strongest signal. I'm certain there's an Android equivalent.
Evernote: Evernote is a must have at any conference, period. It's one of the most versatile ways to capture information, from photos to drawings to audio to text. Sync it wirelessly as you travel and your notes will all be on your desktop when you're ready to start processing them.
Conference apps: Dreamforce has its own app that lets you plan out your calendar. Vitally important to use it if you are attending this conference. In the absence of it, make sure you use a great calendar app to keep yourself straight about where and when you should be.
Uber: If you're working in a city that supports Uber, it's a handy way to get transportation when you need it - at a price. Use the app, program in your location or use the GPS to auto-find you, and you can locate a town car nearby with estimated time of arrival. You'll pay rates comparable or above taxi rates.
LinkedIn and CardMunch: If you're doing any kind of business networking, these two apps are mandatory. LinkedIn's app is obvious, but CardMunch is just as vital. Take a snapshot with your mobile device of any business card, let it process it for a bit, and you'll get the opportunity to find your new contact on LinkedIn and make the connection slightly more permanent.
Square and Square Register: Doing any kind of retailing? Have your Square reader ready and you can process credit cards wherever you are. If you've got something to sell, this makes selling far more frictionless.
Notability: A handy app for annotation, editing, and document signing. Dump the contents of any standard format document (Word, PDF, text, etc.) into it, and you can edit, highlight, apply ink-like signatures to it, and ship it out as a PDF via email and the usual assortment of sharing services.
OpenTable: a mandatory app if you're looking to do any client or prospect dinners, as you'll be able to find local restaurants that can accommodate your group. Obviously, you'll probably want to book as far ahead as you can, especially for a really busy conference like Dreamforce, but if you can't, this is the next best option.
This is my short list. What's on yours?