While there are many clipboard enhancement tools available for Mac, I like to use one of two free ones. The first keeps things simple, but adds that extra dimension that makes your clipboard so much more useful. It is called Jumpcut and can be found at Sourceforge.net.
Basically, what Jumpcut does is to give you a clipboard that is several items deep. With it you can access the menu at the top of the screen and choose to paste in previously clipped items. In fact, it keeps a running record of your most recent copies, and you can choose any one.
The options for Jumpcut are kept simple. You can have it remember more items if you wish, and display more choices if you wish. One limiting factor of Jumpcut is that it only works with text. If you want to use images, you'll need something more advanced like ClipMenu, which can be found at clipmenu.com.
In addition to accepting text and images, ClipMenu also has a more complex menu, including breaking the items into groups of 10 or less and Snippets, which are items permanently available through ClipMenu for pasting.
You'll also find ClipMenu's options more detailed than Jumpcut, with fine-tuning like font sizes in the menu, labels to indicate the type of item, and even the ability to integrate with simple scripts to do things like change the case of clipboard text.
The best thing about Jumpcut and ClipMenu is that they can be used together. Simply install both. They will both remember what you copy. For the simplest of needs I use Jumpcut, and then for things like images or the Snippets feature, I use ClipMenu. And since they are both free and stable, there's really no reason not to try them out. Except that once you have a clipboard with depth, you'll never be able to go back to the single-item 1980's style clipboard again.