What does it take to get prepared for a trip like this

Well people, I am no expert on what it takes to get prepared.  All I know is the tour company made things so much easier by providing a list of things to bring.  For me as a woman, I find it to be exhausting just looking at this long list of things to buy.  With this being a last minute trip for me, there are so many things to get and so little time to do it.  And then you sit and ask yourself questions like, "did I pack the right things, did I pack too much, did I pack too little, if I didn't pack these items can I get them easily down in Australia, will I have enough time to get those items, will it be easy to find the places to get the items.  So many questions, the more I think about it and try to answer those questions, the more anxiety I get.  Ahhh in my mind you can't do everything in one day. You can't answer all those questions at once.  So the easiest thing for me is to take it one step at a time.  My suggestion is to first go through the list and see what things you might already have at home. I will tell you for me, I came to Las Vegas not knowing that I would be going on a trip. So of course I am not at all prepared.  I had to search through my closet to see what I already had and what I need to get. I pretty much had nothing. So I have to start from scratch.