My friends and I had/found this rules we made when traveling, especially when travel with friends. Perhaps you'd find these helpful:

1. Have a joint cash, put in a separate wallet/envelope where everyone contribute the same agreed amount. We had each Rp 250,000.- for starter, which we used to pay for car rent, gasoline, snacks and hotel fare. You can always add more for the group expense but pay separately for the things you consume differently like meals or cigarette. This makes all fair on the expenditure.
2. Make sure you have CDs/USB connecting cable to iPod/iPhone for music. The radio frequency would fade as you go further to the east so better be ready with some music to accompany your trip. Or else you can sing-along together like what we did but it took a lot of energy.
3. It's gonna be 2-3 hours drive from Sanur to Tulamben/Amed. Be prepared for the long way, it will be mix of countryside two-lanes road across rice fields, forests and hills. It will be curvy and up-and-down, but the natural scenery around really worth it.
4. Amed has only one five-meters road along the shore so make sure your vehicle is small enough to park/make a U-turn. We rented a Karimun Estillo and last January I came with an Avanza. Don't bring such minibus or double cabin kinds.
5. You can also go to Amed by public transportation. There are angkot from Padang Bai to Amlapura and Amlapura to Amed, but we didn't go for it so we don't know the details. It would cost much much cheaper, tho.
6. Our hotel rate in Rumahku Homestay (at right side of the road, only few meters after Uyah Hotel) was Rp 150,000 per night for 2 persons + 1 free extra bed with aircon, four-poster bed + mosquito net and open-air shower. Plus a banana pancake + coffee/tea for two persons for breakfast. It was really worth it!
7. Most accommodation in Amed are ranged at this price especially the homestays. You can also find beachfront homestays at just Rp 100,000-Rp 200,000. But there are also expensive villas with better facilities. Make your research before coming or you can drive the whole way to the end of the road (about 8-10 km far) before making any decision on where to stay.
8. Always go out at night and find a spot where there are lack of light and see up. The sky above would be full with stars and you won't regret the walk. It was a very cool experience (especially to urban people) and if you are lucky enough, you could see a falling star. Make the wish!
9. The price for snorkeling equipments are: Rp 15,000 for the goggles; Rp 30,000 for goggles+fins; Rp 50,000 for goggle+fins+safety jacket. These are the prices from Mr. Made at the Kawi Karma.
10. The price for snorkeling with jukung boat is another rate. They offered us for Rp 200,000 for the three of us but I guess it's a little too overpriced so we need to bargain. We didn't go for it. 
11. Amed has splendid view for sunrise by the beach (for it is facing north/east), the magnificent Mount Agung at the west side, some range of hill/mountain and beach/cliff around, and Lombok island at distant. Sometimes you can see Mount Rinjani when the sky is clear and you can always go to the beautiful Gili islands by speedboat.
12. Better to stay for at least two nights in Amed, try both snorkeling and scuba diving, and go further to the shipwreck at Tulamben. Many underwater spots and many PADI licensed parlors, some have package with the room for stay (hotels or homestays). Make your researches and have fun at the easternmost part of Bali!