With the 4th anniversary of G+ I thought I'd go back and look at my early posts. This was stupidly hard. The easiest way was to request a data takeout, unzip it locally and then sort the posts by reverse date modified.

My first public post was about a week after the launch day. It turns out it was a report about looking for features that were in Buzz but missing from G+ 

https://plus.google.com/+JulianBond23/posts/1qBXL7B367V _I've been searching for something in G+ that let's me see all the posts I've commented on. I can't find it yet._

Now it's 4 years later. There's still no way of getting a list of all the posts you've commented on. And you can't get it from Takeout either.