Glenn Lazarus reckons the food he was served at a dinner with the prime minister was lovely, but not enough to fill him up.

So on the way home he made a pit stop at Maccas for a Big Mac, fries and a Diet Coke.

The independent senator and some of his crossbench colleagues were Malcolm Turnbull's guests at The Lodge on Thursday night for what has been dubbed the "Last Supper", in light of planned changes to the way Australians vote for the Senate.

Senator Lazarus and six other crossbenchers are facing a premature end to their parliamentary careers, if the new rules are in place for a double-dissolution election.

The former star footballer - nicknamed the Brick with Eyes - said dinner guests were served blue-eyed cod, that was "gone in two mouthfuls".

"The food was lovely, don't get me wrong, but the portion size was a little on the small size so a diversion to McDonalds on the way home was needed," Senator Lazarus told ABC radio the morning after.

On the more serious side, he dismissed the night as a "waste of time" because Mr Turnbull was unable to satisfactorily answer his questions about issues such as the Queensland drought, coal seam gas and multinational tax.

"All he did was waffle," Senator Lazarus told 3AW.

Independent senator Jacqui Lambie used the dinner to make the case to Mr Turnbull for Tasmania to be given the Defence contract to build new combat vehicles for the Army.

"North Tasmania has the capability, know-how and skilled workers," she said in a statement.