Mix Spider Abs - Get into plank position with elbows locked. Pull your knee towards your opposite elbow, then towards your same elbow, and finally extend it back and out as high as you can. Repeat for 15 reps on each side.
Side Bridge Crunch - Get into side bridge position, resting on your elbow, the other arm extended above your head, and your feet staggered (one behind the other). Bring your back knee towards your elbow, tightening your abs as you crunch. Repeat & switch sides.
Full Sit-ups - Lie on the mat with your knees bent, feet slightly apart, and arms extended in front of you, palms facing up. Do a full sit up, keeping your arms straight and contracting your abs as you come up.