Re: portfolio, we used one for a child just turning five. It included grade three workbook pages done in the child's own printing, artwork samples, video of unrehearsed reading of Shakespeare, and video of the child talking informally about a family history project. I think what you include will need to cater to your child's strengths, whatever they may be.

Consider what it is about your child that makes you (and others) say "wow!" Then find a way to capture that factor.