If you have already started trying Ubuntu 16.04 (which is reasonably stable in my experience) with Unity for non-production usage, you might be missing the ClassicManu Indicator in the repos. Here’s the good news: the developer has released a new version with support for Ubuntu 16.04 a few hours back!
The ClassicManu Indicator utility brings back the good old Gnome 2 style start menu to Ubuntu Unity.
Visit the app’s webpage and download the deb package.
To install, run:
$ sudo dpkg -i classicmenu-indicator_version_all.deb