How to assign hotkeys for pasting from the clipboard

You have two main options for a situation like this.

There are clipboard managers that would help you. They generally don't allow multiple things in the clipboard at the same time, but they do allow you to easily paste anything that has been copied recently. So, you could copy everything you need (individually) and then select what you want and paste it.

ClipMenu is a typical clipboard manager.

The other option is a text expansion utility, which I think would suit your needs better. These are tools that let you type something short and automatically change it to something longer. For example, you could type dd and it would change it to the desktop machine name.

My favorite text expansion utility is TextExpander.

My favourite swiss army knife for OS X, LaunchBar, has clipboard history and management. In addition to being able to access historical, clipped information it can also do clip-merge. A quick double press of Cmd-C will merge the currently selected contents in to the current top-of-the-heap clipboard object for you, allowing you to paste them as one object with a single Cmd-V.

You can merge multiple items in the clipboard history by selecting the first one and doing Cmd-C and then selecting additional items and doing the quick, double press of Cmd-C. They'll all get merged in to the top item as expected.