I automate a whole bunch of stuff and have redundancy on all float switches (not valves - float valves are evil!). IMO the most important is auto top off and I don't have the same issues that Matt has with float switches.
I also try to find people I trust to look in on the tank, and I make things as easy as I can for them like I recently put all three of the skimmer collection buckets on switches that pump the skimmate out so the tank checker doesn't have to lug a bucket. I also have a big tub of fresh saltwater in case its needed, and all they have to do to add water is flip a switch.
I get at least three people on a list ready to deal with problems should they occur, and let people in my local club and local stores know I am going away. For me, people are the major key. For long trips, I get a house sitter and I take time to go through the system with them and leave them a sheet of info on what to do.
I am also currently working on (still working on, trying to work on) a webpage manual for my systems.
And, I gird myself to come home to everything being dead. On the recent trip, I was ready for all the cuttles in the cuttle system to be dead, and there was a problem in the system that got taken care of by a friend, and all the cuttles are doing great and laying eggs.
Remember, I have a big system that I was recently able to trick out and most of it is under the house where a flood won't worry me at all. Big system plus tricks equal generally more stable. Hey - you'll get to see it in a few weeks.
OK - thats pretty rambly. Maybe I will clean it up later. :mrgreen;