I was a light packer until I had kids 
I like to think I get it about right now but it's been a process!
Sorry if I'm repeating anything but you will need:
For the flight: light sweater (air con can make it chilly), e-reader (not books), tablet with pre-downloaded stuff to watch, noise cancelling headphones. Depending on flight timings, neck pillow and thin blanket if you're likely to want to nap.
For the holiday: 2 swimsuits (always helpful to have a spare), flip flops, quick drying towel, goggles if you use them. Comfortable hiking boots or trainers (broken in if new!) and plenty of socks. Basic first aid stuff including plasters (regular and blister plasters), antiseptic cream/spray, paracetamol and/or ibuprofen, insect repellent, tick remover, bite relief cream (and in my case antihistamine tablets as I get allergic reactions to bites).
Plus the obvious clothes and toiletries. Maybe a travel-size sun cream in case it's not possible or convenient to buy some immediately. Sun hat and sunglasses. I always take a big tote bag (for swimming stuff in daytime) but you might prefer a backpack if hiking. I also take a smaller handbag for phone and purse in evening. Maybe one light pair of shoes - pumps or sandals - for the evening, but not heels.
Not essential but nice to have: a power bank for charging devices on the go, particularly helpful for travelling as it's not just the flight but also all the time travelling to/from airport and waiting/queuing while you're there, especially if there are delays.