I would suggest a smartphone. I picked up a
droid X before going to OCS in preparation for Candio phase. It has already paid out big time, and I still have a few weeks to go till that point. Pretty much, I was granted Emergency Leave for a weekend, and it really helped to get my affairs in order at the last minute, being able to browse ticket prices, weather conditions, and call all from the same phone. Then there was using it while waiting for my car ride up to Providence after being granted holiday leave. Pretty much, it's been amazing the few times I've been able to use it, and it'll prove very useful once I become a Candio. Would highly suggest it.
Also, ignore the OCS website when it says to bring a whole bunch of white t-shirts. That hasn't been updated since the move to NWUs, which require blue undershirts. The white t-shirts are only used with the khakis, which you won't be wearing till long after you can detail over to the NEX. I've shredded mine up to either be shoe polishing rags (which they're quite good as), or high-dusting rags, or general cleaning rags.
Bring a lot of socks. Best to have too many than not enough. Same with underwear. That stuff can get quite nasty, especially in your first week. On that same line of thought, buy more blue t-shirts and boot socks from the NEX/uniform shop when you have the chance during your training.
Spray starch is good. They'll make you put it in your lucky bag, and there's a chance your class team won't allow it for some inspections, but if/when you need it you'll be happy you have your own stash one lucky bag run away. Just don't be a jerk and make sure to share with your hatch mate at the very least.