Bringing something to keep you entertained is very good advice, if you're not called at all, or if they have a lot of cases and it takes them all morning to call you, it can be excruciatingly boring without a book or movie or something.
If/when you get called, it TOTALLY depends on whether you want to actually be on a jury. I sat on a 4 day trial a few years ago and it was a miserable experience. It was boring, tedious, made me hate every party involved, took a week out of work and paid almost nothing -- really made me question the whole system (maybe a bit dramatic)... trials are nothing like in movies or TV.
IF you get called and you do not want to sit on a jury, the key is to talk as much as possible during Voir Dire -- that's when both lawyers will discuss high level details of the case to make sure that any potential jurors aren't biased in any way. Find excuses to say something as often as you can. If you want to sit on a jury, keep your mouth shut!
Either way, good luck.
