Hmmm. I think that if you had something to give away for free to get people to remember you and come back when you do have something, it might be worth getting a table. You kind of make a good point - what incentive do they have to come and talk to you if you have nothing to offer? People love free stuff, though!
If you are an author, part of your business is selling yourself and your work. A podcast I've been listening to recently that is geared toward helping people build a business (www.chalenejohnson.com/podcast
- Build Your Tribe) strongly, strongly, strongly recommends starting a mailing list right away, even if you don't have anything to sell yet, and to attract people to it, have some sort of really cool "freemium" - something that is worth paying for but they can get for free if they sign up to your mailing list. It lets them see how awesome you are, kind of a "free trial offer," and has the potential to make them a loyal follower. In your case, it might be one of your short stories. Maybe you give them a free ebook when they sign up for your mailing list, but then when you come out with more books and stories you already have a following you can directly contact to inform about the new book.
Bringing that back to the author table, if you don't have anything to sell or give away of your own yet, maybe you can bring a copy or two of another few authors' works that you really like, and do free giveaway(s) if people put in their business card or whatever in your box. Some sort of drawing. Or, instead of a business card, create your own opt-in form and have them fill in their name, phone number, and email address, and have an area to opt in to your mailing list.
Is it legal to use other authors' works for this purpose? You aren't selling them.