I'm going to Six Flags tomorrow and I'm scared?

i'm going with my friends tomorrow and i've never been on a rollercoaster. i want to go, i mean, like it's something i should do at least once in my life, but i'm still really scared. i know i won't die, but i hate that feeling like your stomach is flying away and i'm afraid i'm going to puke. how can i avoid puking? and what should i wear? i was thinking just baggy mesh shorts and a t-shirt. the weather's supposed to be nice. and how much money should i bring? should i bring food? what should i bring in my backpack? i'm really nervous. sorry for ranting and thank you all sooo much! :)