What should I buy here in the U.S/what should I pack for Thailand?

I am going to be in Thailand for 8 months starting in August. I have never traveled outside of the United States and I don't have any clue of what to expect. I don't know what I should buy here, and I don't know what's available over there. Do they have many American brands over there? Should I be buying most of my lotions, make-up, toiletries over here? I will be staying in Bangkok, if that helps.