i use a Topeak Beam rack with an expandable bag. works great. sometimes it's a little small, but I'd think it makes pack smarter
I carry tow or tubes and a patch kit. Unlike NorCal, we have to put with goathead thorns and Cactus spines.
Take a look at the route - does it have services? The 300K i did in March had no services on a 100K stretch.I had to laugh when I look at the Cue sheet for the Arizona 300K I'm planning on doing Saturday. The RBA (regional Brevet Administrator) had on her cue sheet "limited Services" . there's a store about every 50-60k. The San Diego series had water and stuff at their controls - You were on your own at Cayucos.
How long will it take you? and when does it start? That should tell you if you need lights and reflective stuff.
I also a have Bar Map OTG - I'm not sure if it's available "down Under". I also have light on my helmet that I use to read the map and Computer at night;
Here's my Brevet bike. I've put a different handlebar on it:

and here's my "night rider" helmet: