For our state tests, I make an exception and allow students to chew gum. The only catch is, they have to spit it out once they're finished with their test! Oddly enough, this actually makes some students work longer. :)
These are just little slips I include with the gum to help motivate my kids.
The slips say, "Your brain is so full! It just might pop! "Chews" the right answer! You can't be stopped!"
Enjoy and good luck with testing.