so the data sheets of the various components should be able to tell you how many milliamp (mA) each component draws.
add them all up.
now your batteries datasheet should tell you how many milliamp hours (mA/h) it is good for.
divide the mA/h figure by the total mA draw of the circuitry and you'll get the number of hours battery life you can expect.
this of course assumes that the voltage of the components is the same as the voltage of the battery pack.
if you add voltage regulators into the mix things get more complicated.
linear voltage regulators will convert the excess power into heat.
generally speaking, if you are using a linear regulator you can expect the current draw from the batteries to remain the same as the current draw of the circuitry.
this means that if you are using a linear regulator to drop the voltage of your battery you are wasting all of this power.
switching voltage regulators on the other hand draw only the power that is required from the battery.
you need to use the P=IV (Power = Current * Voltage) formula where the power coming out of the battery will be the same as the power being used by the circuitry minus a percentage for the inefficiency of the regulator. (typically 10 to 20%)
for more info on regulators.)