|I didn't have any on hand for this picture, but you'll want to make sure you include a super-sugary gum in your testing (Bubblicious, Hubba Bubba, etc.)|
Students find the mass of a pack of gum, before and after chewing. Most of gum's mass comes from sugar, which dissolves during the chewing process, so after chewing for a bit, the mass will decrease significantly and students can calculate a ratio. Students can then compare different brands/varieties of gum looking at both the ingredients and the mass ratio.
My students were so excited by the novelty of being allowed to chew gum in class that they very willingly carried out the measurements and calculations, despite the impending vacation (if I remember correctly, I used it before Christmas vacation, but the mindset is the same).
In a similar vein, Tracy, from The Science Spot, has a Bubble Gum Physics activity in which students calculate the speed with which they can chomp gum. You could easily tie this in with By Golly, By Gum and have your students calculate their speed while doing the chewing necessary for the mass measurements.