I'd like to know how to see all of my Google Plus past interactions in one single place. If I go to the "Posts" page I see some past posts I've made. But it seems that some posts are missing and it also doesn't show other interactions such as +1s and comments I did to other peoples's posts.
I don't know that there is a place to see all of your G+ activity.
Obviously the "Posts" section of your profile shows all of the posts that you have made.
Another spot is the recently added "Mentions". It shows posts where your name has been used via
Your +1s show the various links around the web you've "plus oned".
Reviews shows the places on Google Maps (and the former Google Local) that you've applied star ratings to.
The Activity Log available under "Settings" would appear to be the right spot, but from what I can see there's only +1s on posts and pages.
As seen on this other question (How can I find my comment on a Google+ post when no one has commented after me?) it's not very easy to see comments you've made long after you've made them.
So, aside from doing a search on your name, I don't know that there's a way to see all of your interactions. This is obviously not helpful if you share a name with someone who is active at all.