I find quite often when I finished a project on a Half Solder-less Bread Board that I did not use one of the Power Bus Rails. These are attached to the main board with small dove tail joints and a piece of double sided tape underneath.
Then again if I build a circuit on a Quarter size Bread board I run out of space as there is no Power Bus and you have to use "Non Power Bus" holes as the Power Bus.
1) remove the unused Power Bus from half size board,
2) Cut to length to mach the short side of the quarter sized board.
3) Some glue or double sided tape and you have extended the board at no cost.