A MacGyver stoner is a stoner that, according to the movie Half Baked, can make a bong out of anything. The most famous example from the movie involves an avocado.
In my own personal experience, things that stoned people talk about building are not confined to bongs. Given enough cannabis and free time, stonrs can plan to build anything from an anti-gravity platform to a utopian society, and, in any case, know how to Run the whole thing off a nine volt battery.
A while ago, I made a series of highly rated comments on Slashdot to the effect that many stories on Slashdot seemed to be inspired by marijuana, such as "Potato powered Beowulf clusters out of Atari 800s." To be fair, however, if there is any drug that makes people try to run a web server off of a toaster, it is caffeine or theophylline.