I've done longer rides than that, they're not that tough!
Given there's food and drink available you probably shouldn't take too much along with you - maybe a couple of gels just in case. A ham and cheese sandwich always goes down well after 10 hours of sugar-laden energy foods and drinks - sorts your stomach out nicely. Again assuming regular food stops you should stick to water in the camelbak.
Decent bib shorts and a comfy saddle. 10gbp Aldi-special shorts might be fine for shorter rides, but you'll appreciate a proper pair of bib shorts over longer distances. Obviously make sure you've used them a couple of times before the big day. Chamois cream isn't a bad idea, either.
Get some decent long rides in, but beyond 100km (and assuming you're not dehydrated / run out of food) it's nearly all mental rather than physical. So your long training rides probably don't need to be more than 80k.
I'd use a backpack (Camelbak) rather than bottles, unless you've got a really bad/weak back it'll be fine. Clear out all the crap, first - you don't need tools like a chain-checker or bottom bracket spanner in there. A couple of inner tubes, multitool, tyre levers. Check your brake pads before you go, change if necessary. Chain oil can be handy, especially if it's going to be wet.
Try and anticipate the weather - take some sunscreen if you usually need it, after 3 hours riding you'll need to reapply it. You can get small (and stupidly overpriced) bottles that don't weigh much. If rain's not forecast you don't need to carry a jacket around with you. Arm and leg warmers can help if it's going to be a cold start and hot at midday.
Apart from that, same principals as you would apply to a road trip - don't leave your shoes or helmet at home, for example