The best way to get energy is to feed elephants. I have about 200 friends now and most have elephants. I always leave a couple of my elephants unfed so people can get energy when they need it. Each elephants gives 10 energy which is 50 per island. I usually have at least 2k energy to play with so I can focus on feeding giraffes for the chance for more tokens. Problem is I have 120 of my own giraffes and after 4 feeds I still haven't completed a collection. Oh well.
Once you use the elephants you can stock pile food and then when you get low and have no more friend to visit you can buy the dinner from the store to get more energy. Hope that helps