First time to Thailand? What to pack? In my opinion pack as little as possible. Whatever you currently have packed, halve it right now. Considering the climate you’re heading to, having 3 pairs of jeans is nothing but over kill.
If you’re staying in a hotel, most of the decent ones supply some form of toiletry stash, whether it be soaps, shampoo etc. If your heading towards any of the northern areas in Thailand, have a good mozzie repellent is a must. Bushman personal insect repellent with 40% Deet is a great heavy duty one you can carry easily. Better that than getting any one of the hundreds of issues the little mozzie can carry and infect you with.
If your low on toiletry supply, a 7-11 or BigC in Thailand should have any of the things you need cheap. Another must not forget if your taking electronics is the Electric plug adapter to suit your countries power supply. Without this consider all your electronics just heavy useless weight.
For me staying connected to the internet is a must for my work, sometimes it’s frustrating having to just use your Android phone, so taking along a cheap Android Tablet, or even a 2-1 Laptop can be the way to go. Something like a Toshiba Skullcandy which is a great little 2-1, can be awesome as it can also double as a 13.6″ tablet when you’re on the move.
Never forget to protect your credit cards and passport, and having some sort of RFID protection is also considered a must. If you have something like a Pacsafe bag, they normally come with a RFID pocket in them, use it! Also having TSA security locks on your bags can be helpful, they are really only a deterrent, but if a would be thief see’s your bag with them on, and the bag next to yours without them, which one will he pick?
If your using a big backpack for your travels, consider buying yourself a VansClassic Duffle Bag, which you can easily throw your backpack into, saving having your straps torn off on conveyer belts etc when your checking your luggage into the plane.