These were listed in order of importance and most are controlled by breakers.  Sometimes people ask "Why the Transponder?"  It is easier for ATC to keep track of me, after I declare an emergency, while the transponder is on.  If I am at a low altitude west of the Mississippi, I would probably turn it off.  Why don't I need the wing to header fuel pumps?  Because my automatic fuel system keeps the header tank above 8 gallons, more than enough for 45 minutes.  Why the GPS?  Because it is the single pilot's friend.  If any of these systems becomes a problem, its' power can be shut off at the breaker.