The startup is a very awkward situation.
This is a little bit OT but nevertheless should be discussed from time to time.. In one of my designs I needed a relay to switch on the power for the external devices after initialisation of the ports.
This has not only to do with undefined outputs but also with inputs. When external devices are already powered up and the Arduino is not, a much higher voltage (=5V) than Vdd (=0V) is seen at the inputs, which can easily destroy those pins...