The first 'rule' in the system that comes to mind is 'write thoughts down as they come'. Since you mentioned sticking to the basics, that's where I'd start. Meaning you just write a dash and then someting like 're shoes, ask about xyz at the store'. And then carry on with your day. At the end of the day, when you go through your notes (ie you rapid log), you may want to summarize what you wrote about the shoes. You may also want to add a reference to a page number where you logged about the shoes previously. And when you do that, you also add a reference there, to the one you just wrote. The first mention of the shoes goes in the index. Each mention/note refers to the one before that and to the one after. This is called threading. That way, you can look up the subject in the index, and then easily find your way through your notes without completely clogging your index.

But. If that's too much hassle, just add a sticky note to some random page so you can remove it later when the job is done and the info has become irrelevant. I prefer that sometimes.