Try some 'wild rocket', it grows so quickly, you can cut and come again! Also 'lamb's lettuce' is pretty quick, so sow them both in succession and I reckon one growbag will give you enough for weeks! And if you have a square foot left, pop in some 'American salad' (land cress), for the same reason!
You'll probably need to cut holes much bigger that what they print on the bag...
(Answer - get Husband to buy yet another one to go alongside - then you can do the lot, and never run out)!