The Arduino cannot power any of these devices. None at all.
Do not connect anything to the "Vcc" output of the Arduino. The servo will require 6V from some source; either its own battery, or a separate (preferably switchmode) regulator from the battery. It is quite implausible that a SLA battery will be insufficient to power this if it can successfully power the LED strips.
I cannot speak for the MP3 device - haven't done the research but suspect it should not be powered from the Arduino board.
The only other matter is that you have in fact, connected all the grounds from the various devices and power sources, together, preferably at one point on the Arduino pinout.