To simply put it...
Log - log what you are doing, for us that is our homeschool lesson plans with dates of when they are completed or a print out from the portfolio section of time4learning.com.
Samples of work - for us this is a few print outs from time4learning, a few math test from Life of Fred, a few pictures from any hands on projects we have done the list is endless possibilities. But I will include samples from the beginning, middle and end of our school year.
Book List - a list of any and all books we might use through out the year. This is a list of our curriculum books, read aloud books, reading books, any book we might use at all. For us I keep this list in the back of our lesson plan book. That way I don't loose it.
It is really that easy! When I only had one child I would take the time to scrapbook his portfolios. That lasted for the first 3 years. (said with a blushing grin) Now that there are 3 children and NO time to scrapbook, my portfolio is more like a box with samples with the lesson plan book in it.
Here are a few samples from when I did the scrapbook portfolios. To see all of them they are posted on my old blog Strouse Academy.
Love the half pocket page where I could put story starter pictures from Time4Learning.com.