The simplest thing to do is to either make a copy or put the original of a writing sample, math sample, or other student work sample in a file folder and put it somewhere safe where you can find it later. (I added the safe place as a reminder to myself. ) I would also grab a piece of paper to begin to write down books your student has read for a booklist. You continue to do this a couple more times and your portfolio is ready to share with me in 2023. Many families mail the finished portfolio to me, they scan their documents to me, or they upload to the Ohio Homeschool online system.
You can also put an app on your phone to scan items to PDF. Here is an example for Android. Here is another list that shares some Android apps. Here are some tips from Apple support, and an app to scan.
You also may want to take pictures throughout the year of projects or field trips. You can store those in some type of cloud storage as well. The other option is to open up a separate Instagram account. You can add your pictures all year. You are able to keep the account private and just share with me if you would like. Here is more information on setting up a second Instagram account just for your student's portfolio.
Hopefully this is helpful to get you started. If you have any other ideas please put them in the comments. We are all in this together.