I just served on a jury in September of this year (in fact, you can call me Mr. Foreman). I don't think you'll have any problem.
The security personnel are definitely not going to care about your diabetic supplies. As long as you're not carrying a gun or a knife, you'll be fine. At the courthouse where I served in September (I was across the hall from the Phil Spector trial), the sensors were so sensitive that no matter what I did, I set off the alarm every single time I walked through the metal detector. Must have been the fillings in my teeth, because I removed every single metal object I could think of before passing through -- in fact, as far as I could tell, everyone who passed through the sensors set off the alarm. Once you get that juror badge, you will have no problem passing through, no matter how many alarms you set off.
As far as meals go, you'll probably want to take your lunch no matter what the local options are. Courthouse cafeterias are kind of awful, even for non-diabetics. No one will hassle you if you bring food into the courthouse.
Once you're in a courtroom, the judge controls, and in my experience as a lawyer, there is one constant: judges love jurors, even if they sometimes hate lawyers. You'll have ample time to check your levels during breaks (which typically are frequent -- in fact, most jurors gripe that there are too many breaks). If you're feeling woozy in between, all you need to do is alert the judge. I've never run across one who wouldn't be solicitous.
I've served twice as a juror (once before I was a lawyer and once after, which corresponds with once before I was diagnosed with diabetes and once after) and both times I've found it to be an interesting experience. Have fun with it. I sincerely doubt that diabetes will get in the way.