I owned and drove am '04 Prius for several years and got the whole 'hypermile' thing pretty much out of my system. It took all of about a month but I am still mileage conscious.
So now I have this (compared to the Prius) luxury vehicle which gets pretty decent mileage without me even having to think about it.
I also know there is no such thing as a free lunch.
So what things I have control of use the most energy and therefore cause the mileage to suffer the most?
My WAG from worst to least might be:

Air Conditioner
Heater (causes engine to run more to keep coolant hot)
Headlamps
Heated Seats
DRLs
Rear/Side Defoggers
CD Player (volume cranked up)
AC/Heater Fan (higher speeds)
NAV
Bluetooth
Other

 

The AC and heater are certainly noticeable and I'd expect the others have too small an effect . The "ECO" button makes a difference as well. I certainly wouldn't turn off the headlamps to save gas (running red lights will save gas too!).

Some people use the heated seats in lieu of the heater to save gas.

 

Ahhhh that explains it. I have to count to 10 before I can proceed on a green light these days. Those bozos are all mileage conscious and I just figured they were scofflaws. Thanks for setting me straight.

 

Power seats is the one item that you need to add to your list. One power seat adds 80+ lbs to your gross vehicle weight.

 

I was listing existing options. I bet the moonroof weighs a few pounds too.

 

And are you talking existence of, or use of? I mean power seats add mass which decreases FE, but if you have power seats (like the default driver's seat) I'm assuming the question then becomes how much is using it going to affect you. Unless you plan on yanking out the power driver's seat?

But yeah I'd say heat/AC and secondarily fan are most likely to be electricity hogs, running down the battery or requiring the ICE to come on to assist in maintaining charge. Lights, NAV, stereo, bluetooth I'd say are fairly small drains, though of course they all add up. Heated seats I'm not sure, heat generation does take some power. And there's even basic stuff like open windows/moonroof, especially at higher speeds, causing increased drag, to drop FE. But for charge-draining, your list covers most of it. I would personally guess that the fan would be higher on the list--running an electric motor I do believe does do some nontrivial draw. Spinning a CD wouldn't be too tough but blowing air would require some more power. Even at lower speeds, but especially at high levels.

But that's just my guess.

 

I use to work for the co. which make seat assemblies, and I know that the weight difference is less than 20lbs.

 

I had mentioned power seats since I bought the cheaper package in Canada without the leather, moonroof, seat heaters and passenger power seats. Only the heated seats interested me. I also took some solstice in the weight reduction improving FE. I've heard often heard higher weight differences than 20lbs vs power and non power seats. I'm glad to hear that it's probably so little. - I won't feel so guilty for having power seats on the driver side. - Still and extra ~20lb over 300 000 km x 100 000 of these cars on the road does affect the environ. All of our luxury items and safety devices sure does chew up the FE. I won't be ripping out my 7 air bags any day soon to improve FE!

I would be interested in seeing a hycam that had the stock bucket seats taken out and replaced with ultra light racing seats though. - maybe ~100lbs could be shed?

 

I think all the accessories mentioned here can reduce your fuel mileage somewhat. The whole idea is to find a balance of using the accessories you payed for and purchased but with some idea that fuel economy will decrease with their use. Having heated seats, for example............sure beats using them and loosing some efficiency when compared to freezing until the ICE heats to normal operating temperature! AC and most of the other accessories will not have as much a drain on the battery(s). The lights will drain some......obviously, but again they are not something you can turn off at night!!

 

The AC is by far the biggest accessory drain on the NiMH battery — over 6 kW at full cooling, if I am remembering correctly. Don't forget that the AC runs from the high-voltage battery for this very reason! Also bear in mind that all the energy used ultimately comes from the gasoline. The ICE recharges the NiMH battery, and the NiMH battery recharges the 12-V battery.

Stan