The eCommistry package has a default theme which extends the rwd theme that comes with Magento. This is specified in the etc/theme.xml file of the theme.
The default theme adds a template block 'sale.phtml' to the right sidebar of the home page which displays some info about weekly sales as well as removing the base themes paypal image and poll. It also adds a 'creditCards.phtml' block in the sidebar showing an image of credit cards accepted.
The blocks are positioned using the local.xml layout file in default/layout to override and add to the rwd theme.
A second theme in the eCommistry package, called midYearSale, makes a small adjustment to the sales displayed by changing the text and moving the sale.phtml block to above the Home page content, displaying like a banner.
Both themes also add their own update.css file.
It should be noted that creating a local.xml file in the second theme completely overrides the default themes local.xml file, so any changes you want to persist from the default theme need to be copied to new theme otherwise they will not be used. This can cause code duplication so it is a good idea to only make small alterations in local.xml to prevent this.