To read my complete journey to GTD Mastery see the main post.
Step 12 to GTD Mastery is: I have lists for tracking “loaned out stuff” and “stuff I’m borrowing.”
I use ThinkingRock to track these two types of items.
To create a list of my “loaned out stuff,” I go to my Waiting For list and search for “return” as seen below.

BLABLA
To create a list of “stuff I’m borrowing,” I go to my NAs list and search for “borrowing” as seen below.

I use ThinkingRock’s “due” field to store when I have to return the item (e.g. library books) as seen below.

Related posts:
This is a cool program. It is advisable to have a list of borrowed items especially if you are forgetful. I like it.