I don't get this xkcd. If you steal my computer while I'm logged in you can't log into my bank account of you don't know the password. Which bank has indefinitely long sessions? Mine's time out after like 10 mins of inactivity.
The only plausible attack scenario is if you steal my computer while I'm logged into my KeePassX. It has all my passwords visible. But that session times out as well.
There's two didn't attack models, "steals permanently" and "runs code on and returns to you" (which includes both "steals from your hotel room and puts back" or "installs malware on"). Yes, for the first one it's hard to get to the bank account and I agree the comic is inaccurate. For the second, it's very easy to install a keylogger or a cookie-logger or a malicious browser extension or whatever.
Riot installing a kernel module is more like the latter.
title="Before you say anything, no, I know not to leave my computer sitting out logged in to all my accounts. I have it set up so after a few minutes of inactivity it automatically switches to my brother's."
The only plausible attack scenario is if you steal my computer while I'm logged into my KeePassX. It has all my passwords visible. But that session times out as well.