Are you planning to camp?
Do a weekend shakedown tour to test all your gear. You can return home and camp in your back garden at night if you like, but carry everything you use.
The important thing is what to leave behind.
There are any number of packing lists for bike touring which come up on a search engine.
Also have a look at some of the ultra-light camping websites for load-lightening strategies.
I always find plastic bags useful, for waterproofing pannier bags, separating dry and wet stuff, keeping socks dry on my feet.