— User Option: buffers-menu-max-size

This user option holds the maximum number of entries which may appear on the ‘Buffers’ menu. If this is 10, then only the ten most-recently-selected buffers will be shown. If this is nil, then all buffers will be shown. Setting this to a large number or nil will slow down menu responsiveness.

— Function: format-buffers-menu-line buffer

This function returns a string to represent buffer in the ‘Buffers’ menu. nil means the buffer shouldn't be listed. You can redefine this.

— User Option: complex-buffers-menu-p

If true, the ‘Buffers’ menu will contain several commands, as submenus of each buffer line. If this is false, then there will be only one command: select that buffer.

— User Option: buffers-menu-switch-to-buffer-function

This user option holds the function to call to select a buffer from the ‘Buffers’ menu. switch-to-buffer is a good choice, as is pop-to-buffer.