The last two are the jacket and helmet I stick in the pack, and then the pack with the jacket and helmet in it. It's a tight fit for both of them, but it works. Of course, anything you want to bring with you has to be taken out of the pack or strapped to the back of it.
My summer jacket (pictured) is a Joe Rocket textile with Leather elbows and Shoulders. It is fully armored, so I'm guessing it takes up as much space as a typical leather jacket, but it's probably more flexible, so if you want to cram a leather jacket in it might not work, depending on how big your helmet / jacket are.
I still think it's a great pack though, it does wonders for me.
-Mike