The title can be of any length, and search engines will look at your title for information about what your site is all about. They assume that a title is going to be very descriptive of the site. Your customer will be more interested in the first few words of the title.
For instance, you could have just Promotional Products Sales as the title. Your customer who bookmarks this would clearly know what you are when he looks at his bookmark list. Or it could be the name of your company, e.g. Idea Man. It could combine those with the company name first or the descriptive words first. But you don't need to stop there. Add some more descriptive words. These will not show up in the bookmarks because there is only so much space. But the search engine spiders will see them. So, as an example, if you were in the advertising specialty business, your title might be something like Promotional Product Sales - Idea Man - Imprinted Advertising Specialty Products - T Shirts - Mugs - Water Bottles.
Put a hyphen between each idea or phrase. This also helps the search engine to know where to categorize you.
You can change your title all the time. Those who bookmarked you under the old title will still see you that way. But a change might boost you on a search engine.