If you’re installing a Linux system and plan on seperating the /boot folder for the boot loader (which would be rather good) don’t be too excited of how few MB it needs and that it will not change anyway.
40MB, as I have one, it can hold 2 kernels. But on trying to update the Linux system, when it tries to install a more recent kernel, it fails because it does not have enough space.
If you’re gonna install more (linux/unix) systems anyway those may need a kernel as well, as they will probably not all be on the same kernel at the same time.
So be sure to use 100MB, or a little more.