Firslty, make sure you dress as smartly as possible, so it looks like you are taking it all seriously, and are making an effort. This is especially important for you to prove because of your age.

Secondly, you don't need a laptop or anything like that. Print out some of your previous work, but don't simply walk in and say, "this is what I am capable of doing, can I have the job?". Most likely the most important thing you will need to take is yourself, a pen and some paper.

The chances are, the people at this real estate company know very little about the internet, websites, how they work, etc, and probably won't understand nor care for any technical jargon.

Speak to them in plain English. Greet them, sit down, and ask them questions (in plain English - no jargon, or keep it to a minimum if you have to use it). Find out about their business - who are they and what do they do? Ask them what they wish to achieve by having a website. Ask as many questions as possible. The chances are, you will only be talking for a small amount of time - they will do most of the talking whilst answering your questions. Make notes!! Write down everything they say (not word for word, but be sure to get down all of the important points).

As for 'documents' - I aren't sure what documents you think you will be needing. Are we talking contracts, here? If so, you won't have them with you. Contracts need to be written and tailored to each specific project, which obviously cannot be done until after the meeting, as only then will you know what the project will entail. As you are 15, however, you cannot legally enter into a binding contract, so whether or not you will get them to sign something is up to you. To avoid disappointment and/or confusion, however, I would still put together a list of things you will be doing, and make it quite clear what they are entitled to (e.g: revisions, etc), so they can at least read over it and tell you whether they are happy with everything, before you begin work on the project. You cannot do this until after the meeting, however, so personally I don't think you will need any 'documents' with you as such.

What software you use for publishing/printing your documents is up to you. What software you use to make the images for the site is up to you. What software you use for generating or writing the code for the website is up to you. This is not really important or relevant to the meeting, and the customer doesn't care what you use. There are no laws or rules here - you use whatever you feel comfortable using. The most important thing is that you keep the customer updated, and develop a site that caters for their needs, and solves their problems / helps achieve their goals, not just some pretty website containing images relevant to the type of business/industry they are in (which too many designers seem to do - usually the ones which go out of business quickly!).

Keep us updated with how things go, and good luck!