Bentos can be really really simple if you want them to be, exceptionally simple actually! And cute stuff can be kept to a minimum (or, I suppose, not at all, but that wouldn't be much fun now, would it?).
Ben has a stuffed corndog muffin with a cheese airplane on top--one cookie cutter, one slice of cheese, one cut, and we've got an airplane! Behind that, he has some carrot & celery sticks, to go with the little yellow container of dip in the bottom right corner. He has pineapple and blackberries, and a homemade peach/apple fruit roll up.
While I didn't time the actual bento making process, I had the muffin made, the roll ups made, and the fruit/veggies already diced in my fridge. The little cheese plane didn't require a whole lot of mental effort. ;o)