There is a HUGE range of gadgets that you can use to help you train and do the ride.
There was quite a few of us who was going to do the ride and the cheapest that I can recommend for a group of people doing the ride is STRAVA (of BAIKA as it is called on Windows Phone).
This is an app, which is free (or extremely cheap) at the time of writing. It allows you to track your route using your phone GPS, it shows you your speed, the distance, how fast you compare to other riders who have riden the same area, and, if there is a group of you, you can all see how you are all getting on by creating a group.
If you have an Android, Apple device or Windows phone this is the best (and cheapest) way to get started on tracking progress. BE WARNED – USING YOUR PHONE ON A RIDE TO TRACK YOUR SPEED AND LOCATION USING STRAVA EATS BATTERY!
Beyond that app, there are quite a few options. I personally wanted to track my average cadance (speed which i turn the pedals) as that helped me ensure that I kept my level of motion in my legs constant. You track this by buying a widget for the crank arm on your bike which detects when the crank passes a sensor.
Most people would be happy with just current, max and average speed and distance, plus way point and / or lap information. A bike computer from your local store for 20 GBP will provide that.
Garmin do a range of widgets which can get VERY expensive. If your take cycling seriously or want to, then they are a good range to look at. Some allow for maps to be uploaded so you can plot a route on your PC and upload it to the device – like satnav, it will then tell you which route to go.
Beyond bike computers I would suggest lights. If you are travelling back after the ride finishes it will probably be dark. Make sure you have lights.
A day glow top is worth having. Not for your sake, but for other road users. Making sure they see you is EXTREMELY important.
A decent bike helmet which fits and hasn't been dropped should also be purchased.
I bought a bike pump with a pressure value on it. This helped me ensure that my tyres were up to the right pressure (it's normally written on the tyre wall what pressure they should be).
We didn't need a bike lock during the ride, but if you do intend to leave it over night after or before the ride, either take a lock with you or make sure that the hotel / dorm allows you to take the bike into the room.
If you are a bit extreme like me then an action camera or regular camera might be in order. GoPro and a smaller (much cheaper) company called Muvi have offerings. Else, you can always use your phone, but bring a water proof case for your phone in case you drop it or it rains…
Some people had thin water proof rain macks, I didn't bother.
Sun glasses are handy, but wouldn't suggest bringing an expensive pair.