Is it time to put our damned boots on or what ?
You misunderstand how the Convention of States works.
Congress has no part in the Convention, it's enabled by Article V to allow the State Legislatures to amend the Constitution without governors or Congress critters being involved at all in the process.
They first agree to specific amendments, then each State Legislature passes a resolution (without a governor's signature) to participate in the Convention. When 2/3 of the State Legislatures agree (34 States), then a Convention occurs. It is not a physical convention, no one gets together in some convention center to argue it out, it's simply a term used to descreibe their agreement, in exact, identical language in every State's Resolution, Then once they all agree, 3/4 of the States have to ratify it to become an Amendment.
If Bernie advocates free food for all, and proposes an amendment for that, then he would have to persuade a majority of each State's Houses of 38 States to pass it. Not going to happen.