Curious to know the coolest things you achieved by configuring your kernel. I know kernel config can be boring, but I'm hoping someone will have an impressive answer.
For me I have a very lightweight kernel that runs wayland on nvidia without any issues to date.
I used to manually compile with the Linux-VServer patches, before Debian started shipping a pre-patched kernel.
Linux-VServer was kinda like LXC or OpenVZ. I was using it around 2008 or so as LXC wasn't quite ready for use in production yet (was still far from finished) and OpenVZ didn't support Debian hosts.