Arduino Mega and another low power device

Hello, I am using Mega. I have a small device that takes 2.3-3.6V. Is it a good idea to have two separate voltage sources? I may use the 5V pin in the Mega to connect to one more device in the future. Thanks.

Can't you power that (unknown) small device from the Mega's 3.3volt pin (50mA max). Tell us more about the "device", and how you think it should be interfaced with the Mega. Leo..