http://www.supertanks.com/
Replaces the stock tank with a bigger tank.
[Edit] Talking about breaks, I learned that a big tank can cause problems on the trip I just finished. I've driven from Phoenix to N. AL several times without stopping for anything but fuel, food, and restroom. Rough drive, but not too bad till the last 150 miles or so when I would get pretty run down. But the "I'm almost there" kicked in, and combined with some caffeine, and no problem. But I always hated stopping every few hours for fuel "whether I needed it or not". On the way East this time, I had the big tank, and only needed to fill up once on the trip. Unfortunately, I was exhausted by Oklahoma City and stopped for a room. I eventually decided the problem came from several sources.
1) Not stopping for fuel as often eliminated the "walk around and get some blood flowing" part too.
2) Not wanting to be forced to stop at a restroom, I cut down dramatically on my caffeinated drinks.
3) I'm getting old.
4) May also have had something to do with a tire separating and spending hours ratting around in Amarillo looking for a replacement tire in the a.m. on Sunday morning. Didn't want to hit the open stretches between Amarillo and OKC, and then on to Little Rock with no spare.
Not much I can do about #3, and #4 was a fluke (I thought, another story in itself) but I made more stops and consumed more caffeinated drinks on the return trip which helped a lot...