Places to fish, you now from my other comments.
I’d use a 1 or 2 ounce sinker in a standard ledger rig configurations. In the Kaiapoi you could use 3 x 1/0 hooks and get mullet. Or go the next size smaller re hooks.
For bait you could collect cockles from the eastuary at low tide, look for a big area of cockle shells on the surface. Dig below them and you should find heaps of cockles. I’d do this out infront of Caspian St, you may have to walk a bit to the left (along the southshore spit) and out into the eastuary more to find them at low tide.
The area just infront of Main Rd (sort’ve where Rangatira Tce comes down) on the other side of the eastuary is where you can dig for sea worms. You might see patches of sand etc that have been dug up by others there, dig around those areas at low tide. Apparently the best mullet bait you can get.
You could also buy live mussles from the supermarket, they seem fairly cheap and work for bait.
Another place to fish for mullet is on Main Rd (where Cliffs St comes down), there are small jetties there next to a yacht club. You can catch mullet there.
I think the good thing about Fishing in rivers for mullet is you don’t get spotties or dogfish or other annoying tiddlers that can constantly steel your bait. Just into river mouths seems to be the domain of the mullet.