I struggled with some minor stuff with Drupal 7, which I do not think I should be struggling with. However, I found some small modules which helped me solve the problems. I think these small modules should be a part of Drupal 8.
Reset password does not work at the moment
A site I am working on (vih.dk) had a user which could not remember her password. I asked her to use the Forgot Password option. She got her one-time login. However, after using that she could not change her password, as it requires her current password (there is a pending bug). Which she forgot. Not an easy situation. Luckily password_hustle module would ask the user for a new password when using the one-time login. This is how you would expect everything to work in a mature cms, I think.
Shortcut module should be improved
The toolbar is allright. I think many people tend to install other toolbars, and it does not have to be that way. Recently I thought I wanted to use quickbar which is easier to customize per user role. However, I can get the same functionality with shortcutperrole. After installing that I can easily customize the toolbar shortcuts for easier access to some menu items for the end user.
Make it easier to create links
It should be easier to create tabs, subtabs and action links without having to hardcode. I used custom contexual links to create some links there. I used page manager to create some local actions and some tabs. Shouldn't some of those things go into core in one easy to understand module?
So I am proposing to at least get these two small modules into Drupal 8 Core.