Oohh, preparation is one of my favourite things about a holiday. I work out what I will need by starting with anything for which I need special equipment, Swimming, goggles, thermals for skiing, walking boots etc.
Then count the number of normal days, for which I need a daytime outfit snd something go to change into in the evening. Two sets of underwear each day.
On my phone, maybe a spreadsheet, I then work out what outfits to pack, any accessories I want to wear with them and anything else I need to get ready.
Add in the usual phone charger cables, headphones, an extension cable with lots of usb and power sockets, this means you only need one converted for the plug to provide lots of sockets.
Make sure everything you want is clean and set out visible (bed in spare room ideal) so you can see everything. Prune away what you don't need and only put it all in the case the night before you go. Stops you throwing extra things in last minute.
Minimum is my passport, phone, toothbrush and credit card.
I often find myself a tad constipated in the first few days so take some senna pods to make tea last thing.
Keep the list from one holiday to the next, add anything you missed off last time so after a while you can do the plan in a couple of minutes.
Enjoy being a black belt packing ninja