Man-Page:
:~/$ man fluxbox-menu
There are 3 Menus in fluxbox by default.
Menu files are plain text files, line separated and start with [begin] and end with [end]. Custom titles for the menus can be set with [begin] (custom Title).
To open menus you can either define a action in the keys file or use the [custommenu] command to open from another menu.
To create a custom menu, you need to create a new menu file. These are plain, line separated text files, starting with [begin] and ending with [end]. Custom titles for the menu can be set with [begin] (custom Title).
You need this menu file, save it to ~/.fluxbox/menu-exit. You may also need to disable password confirmation for these sudo commands.
[begin] (Exit)
[exec] (shutdown) {sudo shutdown -h now}
[exec] (suspend) {sudo s2ram}
[exec] (reboot) {sudo shutdown -r now}
[exit] (logout)
[exec] (lock) {xtrlock}
[end]
Now add a menu opener to your main fluxbox application menu in ~/.fluxbox/menu.
[begin] (Fluxbox)
... other entries ...
[custommenu] (Exit) {~/.fluxbox/menu_exit}
[end]
Add this entry to your ~/.fluxbox/windowmenu to toggle all decorations on/off.
[begin]
[toggledecor] (Decorations)
... other menu entries ...
[end]
Remember: default keyboard shortcuts allow to open the windowmenu with [Alt+space] as right click on window titlebar will become unavailable with no decorations.