Before you go - planning stuff

Rough itinerary - dont need every hour, just main things you want to do
Budget plan - how much for food, transport, little extras
Emergency contacts - friends, family, maybe local numbers too
Confirm reservations - hotel, car, tours if any, saves headaches later
Check weather - pack accordingly, sometimes one jacket solves it all

Packing essentials

Clothes for 3 days, plus one extra outfit just in case
Toiletries - toothbrush, toothpaste, deodorant, small shampoo, whatever you use
Medications - regular ones and a few basics like painkillers
Chargers, cables, power bank - easy to forget when last minute
Snacks and water bottle - keeps you from buying overpriced airport stuff

Travel documents & tech

ID or passport - depending on where you go
Tickets, boarding passes, confirmations - print or digital
Phone, camera - dont forget memory cards or storage
Wallet, cash, cards - check you have enough for small things

Extras for smoother trip

Comfortable shoes, walking friendly
Light jacket or layers, planes and mornings can be cold
Sunglasses, hat, sunscreen if outdoors
Small backpack or bag for day trips
Relax a little, dont try to cram too much, enjoy each moment