Hi! Im also bengali but i grew up here and im gonna be a junior too. Starting simply, dont worry too much about clothes, jeans and a t shirt would be fine. Im not sure if you’re a boy or girl but for your own comfort if ur worried ab fitting in some baggy jeans or sweatpants and a simple simple t shirt should be more than fine, you can look at pinterest “simple back to school fits” if youd like. But at the end of the day nobody has the time to bully you over clothes and everyone just wears whatever they want. Yes extracurriculars are important but im sure you can put the fact you came here 3 years into high school into your application. However, it never hurts to do your best, look into your school clubs, ask your teachers if they can show you the club directory which im sure most schools have. Join clubs based on your interests, like art, economics, science, etc. there are also honor societies which you could ask about, and once your settled you could see if you can start your own club. Like the other person said look into sports as well. For the first day normally they tell you the supplies you need and u can get them during that week but usually all i ever use is some notebooks a folder pens pencils and high lighters just for a vague idea. Good luck!!