This is a quick tip for something that can create a lot of hassle sometimes. As you may be aware of, it’s impossible to copy/paste items across Publications. One option would be to create them manually, but what if they’re too many?
Another option is to use the Content Porter. Right, the Content Porter.
Few steps:
1) Rename the target Publication to whatever temp name you like
2) Rename the source Publication as the target one
3) Launch the Content Porter, select the renamed source Publication, pick the items and export
4) Rename back both the Publications to the original names
5) Launch the Content Porter select the target Publication and import the package.

VoilĂ !