Here's another possible solution I just stumbled across. So far, I have not had to use any modules, but I was researching modules for adding to the Wiki and came across "Code modules".
Long story, short: You can create a Code module (in the IDE, click Project - Add New Module - Code Module) for each type of code. In the screen shot I posted before of a list of subs, a bunch of them started with b001 through b006e. I could move all those into a Code module by the name of, say, "Bidding", and they would no longer appear in the Main module. Instead, the name "Bidding" would appear below "Main" at the top of the Modules tab and when I clicked on Bidding, I would see only those subs. This, in effect, provides the ability to "expand and collapse" that you wanted.
I did a simple test app to make sure my facts are at least semi-straight and it worked, for whatever that's worth.
Main:
Sub Activity_Create
Mod1.DoSomething
End Sub
Module "Mod1":
Sub DoSomething
MsgBox("Nag, nag, nag.", "")
End Sub
I'm hoping someone will correct me if I have something wrong.