The way I understand it, "strewing" is about planning exposure to various things of interest. In fact, it's about the "ecology" of the unschool, the environment or atmosphere. I guess some unschoolers make a list or schedule of things to "strew" and others keep an idea notebook where they can brainstorm ideas, collect resources, and make plans. Not too much unlike what structured homeschoolers do except that the plans are a bit looser and more subject to change.
One thing I am trying to do, especially for Brendan but also for the other kids, is make a course sheet for each subject and then, AS WE DO IT, write down what we do, rather than structuring it ahead of time. Obviously, I still prepare ahead of time -- it's a little like what I did with Liam.
For example, Sean's already read several ancient history books -- enough for a quarter, almost. If he wants to focus on history, he can do that, and then I can try to give him some science-focused books or projects -- "strew" them. OR a different kind of history, or religion, or whatever.
So I should have a notebook with one section for plans and ideas, one for what the kids are actually doing, and one for observations and journalling; maybe one for philosophy : )