There are some things I would like to mention, although I won't go in details, as the Backstreet Ruby page on compiling the kernel discusses this topic.
You have to follow this order:
Input support
Virtual Terminal support
Console drivers
for all required options to be available/selectable.
You have to use built in input support:
Input device support --> Input devices (needed for keyboard, mouse,..)
Input device support --> Mouse support
I would suggest you also include at least one keyboard (built in - not as a module). You can also use modules, but I find it safer to be able to use a keyboard instead of trying to find a PC with ssh (or something similar) to load the required modules.
For AT/PS2 keyboards, turn on (not modules):
Input device support --> Serial i/o support
Input device support --> i8042 PC Keyboard controller
Input device support --> Keyboards
Input device support --> AT keyboard support
For a USB keyboard turn on (not modules):
Input device support --> Keyboards
USB support --> support for USB
USB support --> USB Host Controller Drivers
USB support --> USB Human Interface Device (full HID) support
USB support --> HID input layer support
If you are new to Linux, do not try to patch an already patched kernel (heavily patched kernels like the ones that ship with most distributions). Use a kernel from www.kernel.org, and take a look at the Linux Kernel HOWTO.
In Backstreet Ruby (the patch for a 2.4 Linux kernel) does not support frame buffer devices , and for that reason is disabled.
In Ruby (the patch for 2.6 Linux kernel) if you want to disable/ change to modules support for PS2 input devices, you have to first activate/enable "General setup --> Remove kernel features (for embedded systems)"