I have several kinds of masks, but tend to use the inexpensive and commonly available ear strapped paper jobs that are blue on the outside - outside!. In our current temperature warm up in Spring and going from car to parking lot to store there are substantial fogging opportunities.

Item 3 of this youtube link It's a bit of a kluge but if I fold up a bit of tissue (such as kleenex) into a thin multifolded strip, I can jam it as a sort of seal above the nose but below the mask, held in by fluffy friction. It will keep exhalations off the glasses, but when I'm back in the car it's soggy.