I did go to Alaska in 2000.
At that time my 2000 Ultra had 1800 miles on it and it was stock with the exception of a Stage I kit and V&H pipes.
I got a little better mileage then but I was also pulling a small cargo trailer which gave me a safe fuel range of 160-175 miles.
I don't think we ever had a stretch of highway more than 100 miles without fuel being available though we had to settle for 89 octane at a few stops.
One of the guys I went with had a metric bike with a huge engine and he was the one worrying about fuel.
My wife rides a Heritage and I think it has a 4.2 gallon tank and she gets well over 40 MPG's and usually we stop at about 125 mile intervals and her bike usually takes about 3 gallons to fill it up.
I've never carried a gas can on a motorcycle but I most always carry a siphoning hose on trips.

 

2012 with Rush slip ons, SE air cleaner and Stage 1 map.

Started when new at 30 to 32. As it gets more mileage on motor... I am up to 34 to 36 and even up to 38 on slower speed rides.

Not great but not terrible either!

 

I did Alaska in 2005 and there was several times we thought we where going to run out of gas a couple just under 200 before we found fuel. My bike had over 60k when I went.

My friend that went with me in 2005 went back in 2010 with his son. He took 2, 2 gallon cans but you see why. This bike had over 220,000 miles on it when he did this trip. Yes we had to put a motor in at 190K but look at the hack it has been pulling since 125,000 miles LOL. This is a picture when he just arrived back home.

 

07 ultra, CSC conversion 30 to 35 mpg 2 up.riding

 

I've got an '03 Fat Boy trike and I'm getting about 35mpg..about to go up a notch with hp by upgrading my 88 to a 95..I've been wondering about what that's going to do to my gas mileage...

 

I have been messing with the AFRs on both our Trikes and have what I consider good all around milage with the maps I have developed, good performance and milage.
My speedos have both been adjusted , most of you may be suprised how far off factory speedos are and that has a effect on what you come up with for milage.
My milage data was accumulated over the course of about a week with all types of conditions. Both trikes ridden at the same time and we were not trying to get milage just normal riding.
My wife has a '10 HD FLHXXX, thats the StreetGlide trike, with a Fuelmoto 107" motor(see my sig) and I have an '09 FatBob with a Frankenstein rear and a 103" motor(I used the jugs and pistons from wifes TG when I did the 107")
The wife gets 35mpg average and I get 42mpg average.

 

I have 2009 Triglide with super tuner and screaming eagle plugs no other extras. Just took trip down coastline to Fla, and mountains on return in Oct. On fill ups computer says best 258 miles, worst 148 miles so to me it's the gas you get .I always use 93 octane and major brands when possible, I think it has to do with amount of additives they put in gas. That's my opinion..

 

After I passed 5000mi and staged my bike (Vance and Hines Power Duals, HD supertuner, and high flow air filter), mileage improved greatly. Not only cooler now with more lower end torque, but I get nearly the same gas mileage as my husband on his 2008 Ultra Classic. It averages the bottom end on high speeds (65+), but highway under 65 it keeps pace with the Ultra Classic. City mileage is still on low end about 32.

I wouldn't trade the ride for anything now on long trips.

 

I know no one will beleive me when I say that lst year I owned a 1996 Ultra with 70,000 miles on it and I was getting 48-52 MPG on it. I now have a 2009 Ultra with a 96" and I get 44-48 on it. Both bikes had been tweaked really well, just something I like to do. My 2009 has SE parts on it, plug pipes, air cleaner and race tuner.

 

Was it a trike thats what I would get on my 04 ultra, but best I can do on the trike is 35 MPG....