This sounds like a cool opportunity!
For me personally, I would do some research about the company. I mean Expedia is pretty well known, but just kind of go through the site's user process. Go through all the tabs and pages. Look for what they do well and what they don't. This way, if they ask you any creative questions like "What do you think can be improved on" or "What do you like about us", you'll already have some ideas.
If you won't be writing any code, then make sure you know the principles of coding; like if you were to teach to a class, would you know how to explain a function or a class object. This way, if they ask you to read something, you'll have quicker understanding. For instance, they can show you a system, and be like "whats the code logic behind this" or "how would you change it". If you're working in groups, then showing team work is important. Showing off your skills is great and all, but boasting and being self-centered isn't attractive. Using your skills to help and work with others in groups stands out more than you might thing the one-man-show does. Collaborate solutions and ideas with people, while taking a leading stance.
Also, don't be afraid to ask questions. Even if you think it might make you look silly or dumb, asking questions shows that you are inquisitive, curious, and motivated to learn. It's an apprenticeship, so it's assumed you don't know as much as them. A person who pretends to know what they're doing is worse than someone who seeks to learn how to do something.
Being honest is good. It shows what kind of work ethnic you have. If you can't stay the whole time, then just tell them. However, I'd say it at the end if you think you did well. If you didn't think you did well (which I'm sure you will!), then maybe when they call or email you for your acceptance, say "Great, but..."