"Arms" is a term of art that predates 2A and the broad use of firearms by a couple of centuries in various laws related to the right of an individual to self-defense against predation by individuals or mobs.
Arms are what is effective and appropriate to the threat against an individual, and so edged weapons and the like are included, as are firearms. When firearms are replaced by phasers, 2A will mean the same and include them.
The basis of the "militia" is individuals, who by definition had to keep, bear and use contemporary arms so that they could be practiced and effective. The arms contemplated there were whatever modern military arms were, so that the militia could offer an effective defense.
Possession of cannon and Apache helos by an individual, as frivolously imagined by some people I have talked with, are outsized arms compared to the fundamental intent of 2A, but IMNHO, possession of an M4 carbine and large magazines would fit. Standard infantry arms. I think grenades and the like similarly would be excessive in the circumstances of modern life, but not so much, perhaps. The Mexican cartels use them...
I am sure someone can provide a more learned response.
Loyalty to petrified opinions never yet broke a chain or freed a human soul in this world — and never will.
— Mark Twain