Hi Southace you are right about the too easy bit !!!!!
The resort at Lizard is very private and does not welcome visitors so it is a no go zone, I know of peole having tanks
filled at the watersports office but at $20 a time so they dont really like to do it. Yes you are right there is no dive shop the last one is back in Cairns I dout if you will get tanks filled in Cook town. The snorkling around Lizard is amazing so very few people dive around there if I was you I would save my tanks to go out to the Cod Hole to dive with the massive cod out there and enjoy the endless reef that is easy to be part of from the surface.
You can get resupplied with food
and that is the same as Flinders Island via Woolies in Cairns and comes up on the barge every two weeks. ( you are in for some new experiances) the Marlin Bar which is the staff bar is open for boaties several nights a week and you can get bistro food
and plenty of beer
but dont plan to buy bulk beer
there as last year it was $60 a case make sure you have your own onboard and visit the Bar just to have a few drinks. There is freash water available.
What type of boat do you have and what size. Good luck Jacko