Got my first booking and need help on what equipment to buy.

If money is tight, I would suggest you rent for your first gig, most rental places will cut you a deal if you rent a package say powered speakers, cables… and have them throw in a simple lighting package with fog. Bargain with them too, they know if they get your business once they likely will get you as a repeat… even if they don’t everyone wins! If money is not an object and you know you are going to commit (and pay back for your equipment) to more gigs: I personally like the Behringer line ofspeakers and at least: a pair of 15″ Mains and a single sub….Quality and reasonable price: They have a few choices and sound quality IMO good as or better then JBL (which I had rented initially) . Do a little reading such as the DDJT link above. You need to know how much power (Wattage) for instance you will want for your future gigs when you buy your speakers …. Don’t go cheap either: Craigslist and E bay for instance have some obscure bands that post awesome specs: don’t be fooled. Go with a good brand and research how much of a speaker you will need. For an 18th birthday, lighting, fog, quality sound and you will be hit / “Epic” if you can spin well and get your crowd going….. this is how I started. My first gig people still talk about it… the lighting and fog machine just add to the ambience… of course the music was the core. Good luck! 🙂

Well, as he said, it’s a 150k drive to get the rental gear, so is trying to avoid that. But maybe it’s worth doing the first time becuase you could use it as an opportunity to ask the rental guys for tips. If they’re nice guys you may get some good advice from them.
Also, don’t be afraid to look at buying second hand gear. There is a ton of it out there and it gives you a chance to buy a good brand, and get extra kit, for the same money as new.