The Gimp toolbox contains some buttons I never use. Because I don't like spilling screen estate, especially on my 1028x800 laptop screen, I wanted get rid of those unneeded buttons.
A first solution (available for Gimp 2.2 and later, I think) is editing the file
~/.gimp-2.2/toolrc. Close the Gimp first if you do this, because the Gimp overwrites the file on exiting and your customizing only takes effect after restart.
I learned another, more graphical solution (also available for Gimp 2.2 and later, I assume) from a video on Jakub 'jimmac' Steiner's blog. In short starting from the toolbox: file > preferences > interface > configure keyboard shortcuts > tools > choose a shortcut (e.g. "F7") for "show in toolbox" and return to the Gimp. With this shortcut you can now toggle the visibility of the current tool in the toolbox.