Combine multiple objects into a single object. Then pull them apart again:
Combine Objects
- Open the outliner (Windows > Outliner)
- Select the objects you wish to combine
- Go to Mesh > Combine
- Combined objects can now be selected in the workspace or the outliner
- Individual objects in the combined group can now only be selected in the outliner
Separate Objects
- Select the combined objects in either the outliner or the workspace
- Go to Mesh > Separate