In case you are experiencing a kernel crash (oops) and have already checked your hardware, you should report what kernel says to the console to [1]. Sometimes kernel crashes so badly that syslogd is not working and what kernel says it never written to a file. If this is the case, you have to catch what kernel says. There are several ways possible.
Manual/Photo
If kernel backtrace is not long enough there are chances that it can fit into a single screen. In that case, you can just make a photo of the kernel crash screen and attach it to the bug report. If you do not have a camera, you still can carefully write down (using a piece of paper and a pen, that is) what you see on the screen, and later type it into the bug report.
Serial console
FIXME
Netconsole
FIXME