(1) Don't tell him that you're having a party to celebrate him turning 16 on the Ides of May. In full awareness of birthday party anticipation anxiety, just say something like "we're going to Bayonne on Sunday to ride bikes with friends."
(2) Buy mini cupcakes, half with chocolate cake (which Charlie does not eat) and half with yellow ('white') cake (which Charlie does eat) so, should he discover what you've stowed away at the bottom of the bag with all the food before you get in the cars, the amount of sugar + rainbow dye #π in the sky he consumes has been minimized. (Sort of.)
(3) Take two cars so you can bring extra bikes and bike helmets for said friends and put the food in the (black) car that you are driving, behind Jim and Chariie in the (white) car.
(4) Remember to get driving directions before you leave so you can find the place where you've put in an order for trays of falafel etc. because some friends could show up early and Mr. New Jersey will need to decamp to the park/party site while you pick up the food.
(5) Don't worry about not having gotten the driving directions because Mr. I Love Driving in New Jersey gives great directions via bad cell phone connection, misspelled text and arm pointing out the window. Plus, you obviously have your cell phone which (as everyone who've been to Greece with you knows) is surgically attached to your right hand.
(6) Don't try too hard to be organized because then you'll set up an OCD mindset that will countervail and ultimately clash with your child's mindset.
(7) Wear something with dark colors just in case you spill coffee, grape juice, baba ghanoush, 'brown drink' or suntan lotion on yourself. (You end up not doing so, but harsh experience has taught you.)
(8) Have the party (that you're not calling a party) in a place that Charlie is familiar with, preferably outside, without fluorescent lights (though don't be surprised if a motorcycle-riding group would choose the same day to assemble in the park parking lot).
(9) Delegate. People do like to help and if someone else can pick up Charlie's habitual post-Jersey City-bike-ride Vietnamese food, ask them. (After making sure you order and pay in advance.)
10) Consult your cousin who has two little kids because, now that you are a seasoned/weary teenager parent (not that you were ever Ye Typical Moms to being with, circumstances being what they are), you have no idea what younger kids (the age of the kids of the friends you have invited) like such as juice. Juice, and more juice.
(11) Keep Charlie's emergency medication on hand because you never know.
(12) Read a Julian Assange op-ed about Google, etc.'s continued evolution into Big Brotherness that Jim suggested you take a look at an hour before leaving for the party. Nothing like total distraction from putting together a social activity for a teenager on the severer end of the autism spectrum in a busy public park near a national landmark (hint: a large statue of a woman with a torch) with bikes, 13 riders, food, drinks and the whole shebang (though you did skip balloons).
(13) Invite lots of people. Friends, former students, colleagues and their kids, Charlie's former and more than beloved and forever remembered teachers who now have their own kids some of whom are the age Charlie was when they taught him at the blue plastic Little Tykes table in St. Paul and St. Louis and he had those big cheeks and wasn't getting shaves from Vince the barber.
(14) Don't worry about anything, whether 90 degree heat, not having enough drinks, the drinks not being cool, not taking more photos, etc.. So long as you have a mostly peaceful easy-seeming boy, it's good.
(15) Enjoy! Revel in the fact that you're all together and that you and your boy have gotten this far on the long road. (And, it's not like you're going to do this too often.)
(16) Order way too much food (inevitably; you're Chinese and your family always has too much food around for any gathering because you are supposed to have leftovers) so you can gladly spend the rest of the week with plenty of hummus.