Electric: Probably a good idea to cut the main switch at the box if the water starts getting in. However, the mains coming into the box would still be live, so if the box goes under water, who know what might happen. Something to look into with the power company or a good electrician.
The breaker box is elevated on the wall at a level comparable with the living area 1 foot above the BFE and level with the road in front of the house. If the water gets up that high we'll be aboard the arc with noah.
Gas: Normally, there is a main gas valve. Make sure you know where it is and cut it off also. Main concern would be stresses on the house causing a gas leak. You don't want that. Again, it might be worth a call to the gas company or certified tech for specific recommendations, if any.
Someoe from the gas company had to come out to the house during the recent cold snaps, he removed some of the old equipment and installed some brand new equipment, complete with an easy to get to shut off valve. The down side is, it's in a lower part of the back yard, water has come up high enough to get over the meter before, whie still not getting high enough to reach even the foundation of the house.
I am not at all familiar with the type of septic system you have.
It works almost like a regular septic system with a few minor differences. There is an initial holding tank where the raw sewage and waste water comes in. This has an aerator, basically a small motor with a long pipe that goes down into the water/sewage/generally nasty stuff. Four prongs at the end of the pipe serve to agitate, or aerate, the stuff. As the solids break down enough, they go through the next stages of the system, which include several filters, a leech bed of sorts, and finally a chlorinator which treats any excess runoff from the system before being discharged via a pipe into the river.
I need to check into whether or not we have a backflow preventor at that point in the system, as it is very susceptible to rising flood waters in the river.