You can add top and bottom sections to the Master Page, and these will appear at the top and bottom of the main content area of each page (unless overridden by the space or page). Like columns, you can add master content to these sections. Static content (e.g., text announcements) will be the same in every page, while dynamic content (macro-generated lists) will be context sensitive.
To designate certain page sections as "top" and "bottom", you'll have to use the Edit Entire Page option in the Page menu. Before editing the full page wiki markup, please read the Administrator Best Practices on this subject.
In Edit Entire Page mode, identify the Zen Section that you want to designate top or bottom, click on it, and select Edit. This will open a "Zen Section Macro" - in the options on the right, scroll down and find "position" and select your desired functionality.
Caution: Carefully identify the appropriate sections to promote to top or bottom. Some sections make up the left or right column, and are inappropriate for positioning as top or bottom page elements.