Hi Bikerbabe! That's really exciting! I did my first half marathons this year - Bristol and Reading!
First things first .. With all the lead up etc my brain wasn't working on the day so I was really glad I'd laid all my gear, gels, bus passes, chip on shoes etc out the night before! Definitely worth doing!
With regards to procedure, each one is different but you usually have your number before so you don't have to sign in on the day so you can just turn up. I'd be AT LEAST an hour early in case of delays in traffic, queues at baggage etc. Chips are usually sent out with numbers beforehand but if yours haven't been, then be extra early in case there's an hour queue.
There will usually be a baggage lorry where you can drop kit you won't need during the race such as the warm coat you took with (take a warm coat/top - you'll be freezing and nervous before the start!), car keys etc.
Definitely take a bin bag. When you've left your warm top at the baggage drop you'll be cold and a bin bag keeps the heat in and you can dispose if it at the start. You'll look silly but practically EVERYONE will be wearing one. I promise 
Start pens should be clearly marked. They're usually in expected finish times (suc as 2:00, 1:50 etc) or number colours or in pace times (9 min/mile etc). If not grab a marshal - there will be loads around to help you.
You should get a course map or race info with your race pack telling you where the water stations and gel / sports drink stations are which will help you plan what to take. However, don't rely on them having what you need - they may run out! better to take what you need if you can carry it! And definitely don't try any new gels on the day ... otherwise a combination of nerves and unexpected sugar can cause dramatic tummy upsets!
Hope this helps! Good luck! Let us know how you get on!!
