Just a basic roll of masking tape and a Sharpie marker.
Labeling all the various flavors of water kefir I have going keeps confusion down. My husband also likes knowing the difference between the salsa and the tomato-basil sauce when he pokes his head into the fridge. Popping a tortilla chip with tomato-basil dip in your mouth is quite a shocker when you where expecting to eat chips and salsa. :0)
This is also great for keeping track of when you put left-overs in the fridge. No more wondering if the food is still safe to eat because you can't remember what night you had chicken.
Do you have any kitchen tips that have made your life much easier?