Is there anywhere a list of questions, answers or comments that I have flagged? I believe a list of such, together with my explanations why did I flag this, should be available, but I could not find it.
You can simply go to your profile, go to the activity tab and click on "n helpful flags". (On the right side, grouped together with the stats such as "people reached", "votes cast" and "posts edited".)
You will get to the list of your flags, you can then choose between various categories (post flags, comment flags, spam flags). You can see whether the flags have been marked helpful or declined. And if there was some response from the moderator handling the flag, the response will be displayed here, too.
Your flag history is visible to yourself - other regular users do not have access to the list of your flags.