Current draw while everything is at idle is very low. That is one of the reasons a switch is not factory installed. A standard receiver will draw around 12mA at idle and a standard servo at idle will draw around 20-40mA.

As mentioned a simple switch ( link below )will bring those figures to zero.
http://www2.towerhobbies.com/cgi-bin...&I=LXVJ45&P=ML

In order to switch off the ESC a switch would have to be placed between the batteries and ESC. This would require the switch to be able to handle in excess of 45A. I don't believe the required work and re-routing the wires would be worth the time investment and increase in total resistance/loss in performance.

If you are able to wire in a switch, you may be able to save around a second or two of run time during your 10 minute walk to the lake.

Ryan