Is already been pointed out earlier and I totally agree, first you need a wall. My reason is that i don't want keys or semi keys in Excellent condition being handled in a box by someone who is rough and not concerned as to how they handle keys day a book with a really difficult dark cover that shows stress lines easily.
And people will be more likely to at least stop and view what you have, at that point if they show interest in a specific book you may be able to suggest other items in your table boxes that might also appeal to them and generate additional sales.
Lastly, I have found my best area of sales at shows lately to be my bosses that are priced at $3 each or 2 for $5. These boxes I fill with anything valued from $5-$25 whether it's Silver, Bronze or Modern but it's usually slow moving stuff. I find the average sale is usually $20-$25 and all I have to do is keep refilling the boxes as new shows come up.
As I stated at the beginning a lot of what I have written has been said already and from what I have read you really couldn't get any better advice than you can from this room full of experts that most have tried every method saleswise and willing to share with you.
Kudo to all for helping out a fellow dealer!