The activity log once again appears difficult by title, but can be done by simply jotting down what the student is doing. It can be done on a daily, weekly, or monthly basis. For the purpose of evaluations, I only require an excerpt of your activity log. Just a small sample (page or two) of your log will suffice for the purpose of your portfolio evaluation. For techies, this can be kept electronically as a file on a computer, tablet, or smartphone. It is as easy as jotting down learning activities on your smartphone calendar and then printing just those activities as your log. I recommend unschoolers take photographs of everything they do; then there is no doubt about what and how learning occurred. One unschooling family made a slide show of their year showing photos for each day. This showed me not only their activities, but doubled as their work samples and curriculum list. I've also been sent links to families' homeschool blogs. These are always informative about all aspects of the student's learning and work perfectly as unschooling activity logs. There is no 'right' way to keep an activity log.
Last
The last thing to prepare in a portfolio are the work samples.