The fad of putting foods in jars seems silly at first (why not use Tupperware?), but it's been a staying one in my kitchen. For one, I know the jar is totally sealed. And since I use jars of all the same size, I have built-in portion control when packing a lunch. True, I usually have to pack a separate bowl along with the jar for actual eating, but that means my desk lunches feel more legitimate.
One of my tried and true jar recipes is Overnight Oats, in which oats and milk "cook" in the fridge overnight to create a sort of oatmeal pudding. I promise it's better than it sounds. These breakfast/mid-morning snack oats are packed with good things, and they can be customized to your heart's content. Here's my basic recipe with a few add-ins.
1 clean glass jar (or another container with a lid)
3/4 - 1 cup oats (I use old fashioned)
3/4 - 1 cup milk (I use almond or cashew or coconut)
1 tbsp chia seeds
The important part is to add enough milk to cover the oats so they have liquid to soak up, then fill the jar the rest of the way with whatever you'd like. A few fun combos:
frozen fruit + spoonful of peanut butter + honey/maple syrup
frozen fruit + nuts (add these in right before eating so they don't get soggy)
frozen fruit + cinnamon + maple syrup
spoonful of peanut butter + cocoa powder to taste + honey + banana (again, add in right before eating)
Experiment to see what you like best, then prep a few on Sunday night to have for the week - my Mondays (and Tuesdays) generally go a lot better when I have some brain food on hand!