Personally I kinda get nervous around compression type file formats. Just me.
But no harm done if you have your back ups.
So if it's OK to use full sized files, I'd just do the "save as" to a USB drive and send that to my friend. Then everything is 100% preserved. This does involve the physical delivery of the drive.
You can also drag and drop the Songs folder to the drive.
Apparently bundle files are good at stripping out un used audio files. Your friend will only get the audio that is used in the open project before saving.
When working back and forth, make sure to keep the original back ups with dates.