This one is simple.
Grab some dumbbells and carry them up and down the stairs. To get heavy enough to really tax yourself, you may need to use lifting straps or the grip will fail long before your legs or cardiovascular system. I like this because of the sequential effort. With stepping or box jumping there is always a point where you can rest. Stair climbing adds a new dimension to leg training - especially if you live on the 3rd floor, as I do!