The title of the question looked promising, but the body then went somewhat off on a tangent.
In the elaboration on the question, it is still assuming that 'reaction mass' is the only way to propel something.
Yes, the laws of conservation of momentum require energy to be input into a system to create acceleration, but they do not require that reaction mass is necessary, nor that the energy source be inherent or contained in the object that you require to be moved.
There are hundreds of examples of transportation/propuldion systems on earth that do not use 'reaction mass'. That is, they have exactly the same mass at the end of the journey as they do at the beginning, without refilling. They mostly use electricity and electrical motors (those that do not depend on gravity to pull them down to earth). A trolly car, for instance, can go a great distance without its mass being changed one iota. Okay, so it is constantly supplied with energy, but electricity is hardly a 'reaction mass', the electrons are returned to source. Tesla's hyperlopp system, where the propulsion system consists of electromagnets in the tube wall propelling the cars, is another example. No reaction mass need be carried at all by the train. Maglev systems are currently in operation using induction motors that require no energy be supplied to the trains. We even have tractor beams under develpoment as serious no-reaction-mass-required transportation systems.
There are also many propulsion systems currently used in space travel that do not use reaction mass. They use the gravitational boost of planets, in a sling-shot maneuver, to boost speed.
As a future-feasible practical example, using electromagnets (as the title suggests), think of a regular, commercial flight path between say Earth and Mars. Along the path, place super-huge satelite way stations powered by fusion ractors or such. They exert a powerful electromagnetic field (or other such tractor beam) along the route, such that they alternately attract and then repel the spaceship along the route. Newton, of course, woukd insist that their mass would have to be substabtially greater than the 'cars' they pull/push, and substantial development would be required in being able to focus/direct/concentrate the electromagnetic field, but this is an engineering problem more than it is a physics problem. Like Ash said in his (her?) answer, it is only a matter of time before the physics and enginnering textbook get thick enough to allow this scenario, first on an within-star, then an inerstellar system.
But the bottom line is, the laws of the conservation of momentum do not demand reaction mass be used for propulsion, just some form of supplied energy.