Honestly how bad does the fog get that you need special kits or a hairdryer like @sean_green44 said. It's just a bit of condensation, right. A quick wipe with your shirt seems to fix it most days. Are people making this into a bigger deal than it really is. Seems like a simple fix should be enough without buying anything.
Watched my cousin struggle with a foggy camera lens last winter. He was trying to shoot wildlife in the cold, and nothing worked. Tried wiping it, but it just smeared. Then some old-timer told him to breathe on it and use a microfiber cloth. Cleared up INSTANTLY, and he got the shot. Makes you wonder about all the fancy gear we buy when simple tricks do the job.
My cheap camera fogged up so bad last week I almost used my whole shirt like lee_thompson said, but then I remembered I was wearing a tank top. The vinegar trick is a lifesaver.