What is an easy way to drain a laptop battery to 0?

apt-get install stress - a utility specifically designed for testing CPU and other functions. You can use it to peg your CPU at 100% usage until the battery dies.

I'm not sure what options exist to peg GPU usage at 100%.

You should drop to runlevel 1 and dismount all volumes possible since your system will not shutdown smoothly.

Run lots of Virtual Machines

Do a full ls -Rlath /

Try to find a string of text within every file on the disk

Fun full screen games