Content Management Systems (CMS) enable you to easily place, and change, content in specific areas of your website. There can be multiple areas, and they can be placed almost anywhere, within the design constraints of the site.
Posting updates of new products, upcoming sales, general news items, etc., will keep your regular customers informed, and help bring in new customers.
One of the systems I use, PulseCMS, can also incorporate a light weight blog and an image gallery into any standard website.
Unify from Unit Interactive has a unique and intuitive user experience which allows you to directly edit the content of your website without the need of any sort of backend admin area. You simply go to your website, and when you login to Unify the editable regions of your website become visible. You then edit the selected content in a popup window.
The other system I use is PulseCMS. It has features such as a flat file blog system (it requires no data base, thus greatly simplifying installation and maintanence), as many photo galleries as you want, as well as the ability to edit content within your websites pages like Unify.
If you already use Twitter or facebook, I can embed the feed from either service into your website. Both the The Village Gun Store and Wes Ward Auto Repair have a facebook "badge" on their websites home page. This gives website visitors who do not use those social networks the ability to see your posts, and if they are members, it will encourage them to friend/follow you.
If you are not currently using either of these social networks right now I would encourage you to check out Twitter at least. It's much easier to use and setup then Facebook and doesn't have the privacy concerns since very little beyond your name and an email address is required to setup and use.