The shelter only works as a system: fly, body, groundsheet and pegs suited to the ground you will actually pitch on.
Warmth comes from the bag and the mat together. A good bag on a cold, thin mat is a bad night, full stop.
Water is the heaviest decision you make each trip. Do it deliberately, and store everything sealed against animals.
UV is the most underestimated risk on an Australian campsite, and dusk is insect o'clock almost anywhere east of the ranges.
The items you hope never to use, checked before every trip rather than discovered during one.
Cheap items that cause the most miserable weekends when missing. This group is why the list exists.