Of course this is different for everyone, but here’s a general checklist you can use.
Clothes
You have to pick the clothes, depending on the weather and season you're going (summer/winter).
Footwear (comfortable shoes, sandals, dress shoes, flip flops)
Hat
T-shirts (long sleeves, short sleeves)
Long pants (jeans,...)
Shorts
Tank Tops
Capri Pants
Dresses
Coat
Sweatshirt
Fleece sweater or jacket
Socks
Belt
Underwear
Sleepwear
...
...
Practical
Charger(for cell phone, camera, extra batteries ...)
Converter
Adapter
Sewing/repair kit
Zip locks bags (they always come in handy)
Travel iron
Flashlight
Travel alarm clock
Day Trip Backpack
Foldable bag (for shopping, ...)
Laundry bag
...
...
Toiletries
Comb/brush
Hair accessories (clips...)
Hair products (hairspray...)
Toothbrush
Toothpaste
Dental floss and mouth water
Deodorant
Soap
Shampoo
Body lotion
Mirror
Soap for laundry
Nail clipper, nail file
Shower cap
Hairdryer
Cotton balls
Cotton swabs
Tweezers
For Her
Perfume
Make-up
Day/Night cream
Nail polish and remover
Razors/Epilator...
Personal hygiene items