I suppose if you have a perfectly flat nose, any sleep mask will do. Otherwise light will creep around your proboscis and wreak unholy havoc on your melatonin production cycle.
But this super comfortable mask ($(removed) on Amazon) does a tremendous job of blocking out light. Judging from the above photo, it even looks like you can drive on a sunny day while wearing this mask without fear of circadian rhythm disruption. It also comes with earplugs, but I don't like earplugs so I can't attest to their efficacy.