The smallest Arduino is the Pro Mini, about 1.3x0.7" board size. Minimal peripherals so pretty power efficient.For display best may indeed be a monochrome LCD, those take almost no current and are readable in most light situations except total darkness.
Thanks. I had looked up micro view, my concern is , whether it will be able to display 3 lines , and secondly its a little costly . Can you suggest a small and light weight LCD display.