There was a most excellent comic adaptation by Marvel in the early 90s. They did the second movie, and then 12 issues of their own original stuff. The tone matches the movies and the art is some spectacular 90s cartooning.
The best part is that the comics were reissued a year or so ago and you can buy it on Amazon right now!
I swear I'm not a cooperate shill. I found the Bogus Adventure issue at an antique store, thought it was funny there was a Bill & Ted comic, and bought it. I only watched the sequel once so I didn't remember much of it. The comic was hilarious, and I really dug the artstyle. Then I found out Boom! Studios was doing a rerelease of the whole run, and preordered it right away. Highly recommend. Comes in a nice hardcover. The print quality isn't HD because something about how they could only manage to scan some older comics and clean it up the best they could. I still think it looks great, but I also don't mind reading old comics on cheap paper stock, so whatever. Don't let it stop you from a great run of comics though!
There are brand new Bill & Ted comics coming out now (since last year), but I haven't read any of them. It's not the original team from '91, and reviews state that they just aren't as good (in comparison to both the original movies and the old comics). Kind of a shame, but maybe the quality will get better later on? Who knows.