In the latest A3 update, BI introduced the "custom compositions" tool for the eden editor. This tool allows any user to save, edit, use, and share their unique or time consuming creations between missions or computers.
To create the composition, right click the things you would like to make a composition and select Save Custom Composition. You can then name the composition and the category it will show under (structures, men, etc). You can also edit the header or delete the composition if you do not want it.
As mentioned before, these compositions are saved in your documents\Arma 3\compositions folder. You can share the folders located in the compositions folder, which should also have the same name you gave the composition in-game.
So no more copying from one map to another, having to share the sqm, or just giving parts to other people.
The attributes are also saved, including the init box, name, rank, etc. This tool is perfect for bases, orbats, module configurations, etc.