For my home electrical power plan I used the 6 circut APC UTS6H which supports 3 power sources (city, battery and generator). I have one circuit set to run my main lights off of my APC 1000 battery, that cuts on automatically in about 3 seconds if the city power goes off. 

The other 5 circuits are set to run off of the portable generator in a load sharing configuration.  When the power goes out I have to manually start the portable generator an plug it into a plug on the back of my house that is wired to the APC transfer switch in the basement. This means that if the fridge and furnace are running off the generator and someone turned on the microwave the APC will turn off what it needs to so the microwave has enough power. The fridge is set that it only needs to run 15 minutes each hour, the same with the freezer and furnace. So the APC can turn them off if something else needs more power.

APC Transfer Switch featuers explained Video

Video of Honda 2000 generator with APC UTS10Bi transfer switch

APC store link

Voltage Drop

Installation next to Breakers

UPS for battery operation

Control Panel

Average Annual Duration and Frequency of Power Outages in the U.S.

For Utah

Utah historical power outages annually

• Avg. Duration w/ Major Event Days: 2.08
• Avg. Duration w/o Major Event Days: 1.23
• Avg. Frequency w/ Major Event Days: 0.80
• Avg. Frequency w/o Major Event Days: 0.61

Generators

Yamaha EF1000ISC 1000-Watt Portable Generator

It has a very small fuel tank but the generator indeed runs for 12 hours on economy mode. This is with 0.66 gallon tank!  So 5 gallons would give you 7.5 tanks each lasting up to 12 hours depending on load.

Can run lights electronics and charge, but NOT big enough to run Freezer, Fridge, Microwave or large furnace

Champion 100158 2800W/3100W Portable Inverter Generator 

It has a very small fuel tank but the generator indeed runs for 8 hours on economy mode. This is with 1.6 gallon tank!  So 5 gallons would give you 3 tanks each lasting up to 8 hours depending on load.

Can run lights electronics and charge, and can run any two of Freezer, Fridge, Microwave or large furnace at the same time. (Note: while running the large items the generator uses gas faster) With load sharing on the APC you can have everything connected and program it so the furnace runs 15 minutes each hour and the Fridge and Freeze run 15 minutes each hour but the Microwave runs on demand.  I have the lights set to run off of battery as well.

So basically with 5 gallons of gas I am in pretty good shape for 3 days of power outage.