This is one of the things I am finding hard to deal with. I am used to a classical programming environment where it's really easy to cut n paste snippets of code from a prototype or other project to your current project. C2's IDE really limits workflow in this area.
It is possible to copy/paste from sheet to sheet and also across different instances of the editor, but you must make sure that any variables/objects that are referenced by the pasted code have been added to the target project.
Not sure if this helps, but are you aware you can include event sheets in a layout? If you tends to reuse a lot of common events (like the bulk of the game's engine) you should make those part of your master event sheet to include in all your levels.