Yay, I can help you learn gym stuff and you can teach me trials
Ok, firstly you are going to want to invest in a powerball (it's those little balls that you spin in your hand) because that's going to increase the strength and fatigue resistance of your wrists and forearms which ultimately means you will be able to grip the bars better and for longer.
For triceps and upper body, you can get on a rowing machine and do a lot of distance at a low intensity. That again, will help the fatigue resistance of your upper body muscles. If not a rowing machine, some gyms have hand cycles (it's like riding a bike but you use your hands instead of your feet) that will do the same job.
If they don't have one of those machines (which I'm sure most gyms do!) then you are going to want to do weights, exercises like tricep pulls (you can find exactly how on walls in the gym, ask a personal trainer or I can show you if you come worthing on sunday:D) pull ups, chest fly's or chest presses will also be good.
Basically though, because you are training for endurance and not strength, you want to keep the weight low and the reps high
Also, as for drinks - you could probably benefit from something sugary when you ride as this replaces used glycogen in the muscles, hence why I drink strong squash