Y2K986:
How much current does the arduino uno need?
Keep in mind that none of the voltage pins will be used ( 5V nor 3.3V ), except for 3 pins for data. All other electronics will have their own power supply.
According to the datasheet the ATmega328P needs about 10mA, there's also a Mega168 on there so that's another 10mA ... plus some other bits and pieces. I'd guess under 30mA total, but the only way to be sure is to measure it.
nb. The output pins can add up to 40mA each when they're outputting a HIGH so add in whatever you have connected to them.