Fill the bottom of the jar with small non-squashable things like nuts, dried fruit, pretzels, candy, chocolates, etc
Add some taller items, things on skewers, and vegetable sticks (get the kids to thread skewers for you).
Fill the rest of the glass, soft items like berries are best at the top, and boom you have Charcuterie in a Jar.. . Jarcuterie!
Notes
Prep in bulk ie set the kids up to skewer a whole lot of things, cut veggies into sticks, then lay out all the options you have and it is quick to build the jars!
You don't have to go savoury, you can make super cute dessert jars too with!
Your jars do not have to all be the same! If you have jars for specific people labelling them with a Christmas gift card would be a very cute idea!