You can buy star ferry tokens with cash at the pier.

if you want to do something cheap-ish yet local, why not have some takeout two-choice rice by the pier ?
it will be way more exotic than lounge food, will not even set you 50HKD back, and you can have it at the pier on the island (I’d recommend wan chai rather than central for this).
Then go to TST with the ferry to watch the show.

Your schedule is tight enough, I would not add anything time-consuming.