A fuel launcher somewhere in our solar system, could throw the fuel out in front of where the ship is going to fly. The ship scoops up the fuel as its going along and uses it to fuel the engines. This has several advantages. The ships engines only need to accelerate the ship itself. The fuel is accelerated up by the launcher, and the ship would only need a fraction of the fuel it would otherwise.
Problems are that unless the ship is flying to a starsystem with a operating fuel launcher.
It can't fly any faster then a speed it can decelerate from using its onboard fuel reserves. Also, this only works when your close enough to the launcher that it can accurately launch the fuel to you. Once your out of range, your stuck with the fuel in your tanks. Which improves the ships power to weight ratio significantly. But the systems are difficult to do, limit range, and don't seem to help us to slow down.