Lately it’s Big Red + generic flavor Bubble Tape. Before that it was bubble-yum + fake-sugarified Orbitz.
When the flavor from the first has just about faded, I throw in the second, for a mouthful of return.
It helps if gum #1 is a great bubble blowing gum, and gum #2 is a long lasting and/or strong flavored gum.
Gum keeps me awake while I’m driving. I guess it’s all the mouth exertion. Or something.