Stifling a sneeze may be the purest, simplest body hack. We’ve posted a couple methods before (pull on your nose, put a finger under it, or bite your lip), but I’ve always relied instead on pressing my tongue on the roof of my mouth. (You can also tickle instead of pressing.)
Source: LifeHacker – Stifle a Sneeze by Pressing Your Tongue on the Roof of Your Mouth