How to have clipboard holding many entries available simultaneously...?
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.