I do the portfolios in a scrapbook style.  This way they have a keepsake for each year.  I divide it into sections: Math, Language Arts, History/Geography, Science, Physical Education/Health/Critical Thinking/Art.  For each section I make a divider page and it list the resources used for that subject.  The hardest part for me is to remember to take pictures so I have them for the portfolios.  I have boxes for each kid that I put papers in that will be used for the portfolio.  As they finish a topic I glance through the papers and place the ones I want in the box.  I keep a list of all the books they read, the field trips we take, videos and tv shows they watch, and I also have a sheet for when we use unschooling methods.  Here are some of the forms I use for records. 

Field trips

Unshooling record keeper

 Here are some photos of pages in the portfolio.

This is a history page

This is a Science page

This is an art page.  I take pictures of all their art projects so I don't have to keep them all but they still have them.

This is a critical thinking page and 1 page of our field trips

That gives you a pretty good idea of the portfolio.  This is their "yearbook".