Measuring the external memory power consumption in FPGAs?
Power analyser tool estimates the power consumption by the FPGA alone due to all the connected peripherals. To calculate the power consumption of the off chip peripherals, datasheets are really your friends  


Consider all static power consumptions  
Calculate dynamic power consumptions due to switching load (\$n \times V^2 \times f \times C\$)
how exactly to calculate depends on teh applicaiton, components and the usage  
For example, if there is an external flash, you can calculate current needed for a simple read, fast read, idle condition and write at particular planned clock frequency. and then, estiamte how much percentage each task will happen over a period of time. the current consumtion than can be scaled accordignly.  
Also, consider quiscent current for deivces which are not switched during operation  
Other loads such as toggling LEDs, RF transmission etc      


All theory can be well verified with practical current mesurement. Consider datasheet maximum for worst case.