You lack the physical material - the actual book - to promote your works when you go out to any author signing events.
The work-around for that is to have at least one thing published in book form to have on the display table, and then having posters and bookmarks and handout items like pens or notepads at the ready for people to take home.
So there's a cost to that: getting bookmarks printed with professional stock paper - glossy stock, a thicker card-like stock - gets up into the tens of dollars to print a hefty amount to hand out.
The rules of creating things like bookmarks are relatively simple:
1) Eye-catching image on one side of the bookmark, usually a part of the book cover art;
2) The other side of the bookmark has to contain brief Author information, and detailed Book information about where and how it can get purchased. ISBN number, which website to find it at, which eReaders can open it, etc.
3) If it's an object, like a coffee mug or pen, it depends on the amount of space you're working with. A coffee mug or mousepad or poster should have more than enough room on one side for the book cover, but a pen or smaller object would have to go with just the title of the book, author info, and weblink to an Author's Page.
Like all graphic design projects, it would help to rely on someone trained in marketing design and layout.
Just to note all this as I prep for the Local Authors' Signing this Saturday.