If you have a PlayMakerGlobals.asset that you want to keep in the new project, then you need to merge in the globals from the old project:
- In the old project, use PlayMaker > Tools > Export Globals
- Copy the Assets\PlayMakerGlobals EXPORTED.asset file to the new project
- Open the new project, use PlayMaker > Tools > Import Globals
If you don't care about the globals in the new project you should be able to just copy the globals asset over.
If you need to move a scene over, export it in a unitypackage and import it into the new project. Just be careful about pulling in lots of unwanted files with Include Dependencies.
I'm looking at doing some kind of automatic backup in the future. However, version control really is the way to go, especially with Unity and it's interconnected asset structure. With version control you can see what files have changed, you can revert changes, roll back to old versions, branch to try something out etc.