‘Nothing to Sneeze At’ means something that is not an inconsequential matter, not a trifling thing.
Example of use: “When Daniel was chosen to be valedictorian, he was so proud, because the honor of being chosen to represent your entire class is nothing to sneeze at.”
In the 17th century, sneezing was considered a symbol of status as people believed it cleared their head and stimulated their brain. Soon sneezing at will became a way to show one's disapproval, lack of interest and boredom. The first recorded use of the phrase in its current negative form, was in 1799, in a play by John Till Allingham: 'Fortune's Frolic': "Why, as to his consent I don't value it a button; but then £5000 is a sum not to be sneezed at."