1. I honestly don't know what limits are you considering for the item summoning ability, but as I am myself quite familiar with such topics I'd consider asking Asterion to focus on his happiest memories and then materializing them in form of a book, or an album. He could constantly carry it on his belt or maybe on a chain. And then, at some point of the story you could have a peek in it and see that the last page is "yourself standing in the doors of the dark storage room".
Or maybe just this:
https://en.wikipedia.org/wiki/File:Pini-plombe-orig-II2_316d_3.2.jpg
It's a jasper seal with cretan hieroglyphs.
2. At first I sent him out because I didn't believe Asterion that the torment he received from Argos was worse than eighty years alone in a locker with a half of your face blown away. I reloaded immidiately and kept him safe the next time. Though I'll have to admit that I'd play the sadistic route when it's a bit more developed (out of sheer curiosity).