It's no secret I love Sportsters, (read my Why the Sportster is the Best Harley Ever Made argument if you don't believe me), but if there is a chink in the armor, so to speak, it would be fuel capacity. Those small tanks look rad and are out of the way when you're ripping gravel roads or hooligan tracks, but when you're trying to put down some miles they can be limiting. So here's a few ways to solve that problem.
The longest-term solution is a tank swap. Over the years there have been a few different Sportster tanks, but the most common are the 2.2 and 3.3 versions. The 2.2 is my favorite one but obviously holds the least amount of fuel. An easy bolt-on solution that keeps the aesthetics of your Sporty if your bike is equipped with a 2.2-gallon tank is to just swap your tank to the 3.3 version. If you're looking for more fuel capacity, the aftermarket provides in the form of Fat Bob-style tanks that hold up to 5 gallons. Something to consider with the Fat Bob-style tank is that it is going to change the look of your bike significantly and it may require some sort of dash also. There are a few things to consider when making the swap.
1) Is your bike fuel-injected? If it is you will need a tank that's equipped to hold a fuel pump. On the underside of the tank you can see where the fuel pump is bolted in and if you have an FI bike you need an FI tank.
2) If your bike is carbureted you just need to get a tank with the fuel valve (petcock) on the same side. If you don't you could have clearance problems depending on your year or model.
3) What year and model is the bike? Without getting off into the weeds, an easy rule of thumb is that most of the Evo Sportster models' gas tanks bolt right up to the frames of other Evo models (1985-2003). Rubber-mount models (2004 -present), the same rules should apply.
The temporary solutions are a plenty but can get a bit sketchy. I don't recommend strapping your lawn mower gas can to your handlebar with a bungee cord, or anywhere else, for that matter. A patch of gravel in the road could turn you and your beloved Sporty into a fireball sliding down the highway.
In my opinion the benefits of owning a Sportster far outweigh the occasional extra gas stop.