1. Long riding days on tour requires electronics with good battery endurance. After being disappointed in the battery life in several rechargeable gps devices, bought a wrist mounted Garmin Foretrex 601 as my biking and hiking computer. Outstanding battery life using two AAA batteries (we use either Eneloop brand rechargeables or Energizer Ulimate brand lithium disposables) Can pair using Ant+ to heart rate straps (and other things that we don't use). It's something of a general purpose GPS unit but meets most of our needs and I am very happy with it.
2. Dynamo hub wheels and LED lighting. We have bikes with Schmidt, SP and Shimano dynamo hubs. All three brands work well and make bicycle lighting something that requires little attention. Yes, they add weight and sap a bit of speed but, in our case, it's an acceptable trade.
3. JBL Wind bluetooth speaker, radio receiver, mp3 player. I'm not much for audio entertainment while riding, but my tandem partner enjoys listening to music or an audiobook. We picked up the JBL in the Auckland airport duty free shop when leaving NZ for about $30 which was a good deal. It does have a sealed rechargeable battery, which I consider to be less than ideal, but it works and when it dies, I get the silence I prefer.