Congrats!! Just remember you need to FINISH–it doesn’t matter what place you are, since it’s strictly a Cat 5 race. Keep an eye on what wheels are out there, and avoid the sketchy ones. Keep your hands in the drops. It’s your responsibility to protect your front wheel.
You don’t need to bring the receipt–they should have the copy of your registration there, since you prereg’d. I’m assuming you did a one-day license. Were you able to do the license online? Or do you have to do that in person? Bring ID so they can confirm you are who you claim.
If this is your first crit: take anything off your bike that could fall off. That means no saddlebags, no pump, no lights. Cameras like GoPros are ok because they’re usually bolted on. Check your tires ahead of time. You can have a bottle, but you really don’t need one for the short duration of the race (especially given the temps). If you really want a bottle, only put a couple of inches of water in it.
As the first race of the day, you’ll be able to warm up on the course. That will give you a lot of time (in the dark, unfortunately…) to check out the course. What I normally do is warm up on the trainer and then do a few laps on the course, but several of my teammates prefer to just warm up directly on course if at all possible. With such an early start, it’ll suck, but just plan on getting there really early to get set up. At least you’ll get an awesome parking place!
Also, I know you’re busy, but if you can make it to the Early Birds on Sunday in Fremont, I’d highly, highly recommend them. This Sunday is the last one in Fremont, but they’re having some others in February. Let me know if you need more details.
Finally, don’t forget your shoes, helmet, and bike. 
And, HAVE FUN!!! 