I basically do the planks as sideways pushups. Adds definition to the oblique abdominal muscles- your sides, where your abdomen meets your hips (the ladies love it when you've got a crease there). I guess you could also just hold it for 20 seconds or so on each side though.
3 bowls a night a the low end isn't bad but maybe try cutting it down to 2 or even 1 if you're worried about health/tolerance. Will be a period adjustment but totally doable if you're getting strong strains. I remember getting used to 1 bowl a night and my tolerance got so low that I was pleasantly surprised by how strong and sustainable the high I was able to achieve from a single bowl was.