In a previous question, I asked whether a flashlight can accelerate me. The answer is yes. This has led me to wonder, this is inferior to all other known propulsion methods in all aspects except one: Shooting light (photons) accelerates the shooter without ejecting any mass. This means we can space travel forever, assuming we have enough electricity.
Are there any other ways to accelerate without losing mass? Note that there are lots of way to do it with external forces like laser propulsion, but I am only interested in doing it without those. e.g. consider a spacecraft swimming in the void trying to accelerate.