Because it is becoming increasing difficult to protect regular computers it makes sense to store sensitive or irreplaceable data (our important STUFF) on removable devices that can be used only when needed. By using these removable devices we are PROTECTING our STUFF. We searched for an available way to say "PROTECT STUFF" that we could trademark. "Tego" is one of several ancient Latin words that can be used to mean "protect", hence the TegoStuff drive.
If you would like a unique explanation on the concept of "stuff" and you don't mind hearing some risque language, you may enjoy listening to "George Carlin Talks About "Stuff".