Its been a long time since I played around with 'ray gun' circuits but a simple one can be made from a 555 and a few other components.
This one doesn't really need an on/off switch. R1 and C1 form a simple charging circuit. Once C1 is charged (apart from a small leakage) the current taken from the battery is minimal.
The switch needs to be spring loaded (trigger switch) so it returns after 'firing'.
R2 limits the current through the LED to a maximum of about 10mA. The 555 is connected as an astable oscillator with R3 and C2 determining the frequency. (these can be changed to suit). The output of the 555 is AC coupled to a 64R speaker through C3. (If there isn't enough volume you can try taking C3 out and directly connecting the speaker.)
When the trigger switch is closed the energy stored in C1 turns on the LED and energizes the 555 oscillator. The voltage across C1 will decrease quite rapidly causing the the frequency of the 555 to fall (a sort of voltage control monostable pulse) giving a 'pew' type sound.
To reload the trigger is released, the capacitor charges and you're ready to go again after a short charging time (R1C1)
For a 'machine gun type effect' operation.
C1 can be charged by a low frequency 555 astable (around a few hertz with say 80/20 space mark ratio). This 555 would be operated by a push to make switch connected between the 9V supply and pins 4 + 8 of the IC.