La Palma is one of 13 Canaries Islands.
Wild camping is possible even when it isn't too easy to find plane places. There is some couchsurfing and helpX. In Santa Cruz you can find a free spot, its a big property where people come and go all the time. You can find a description how to get there on trustroots.
Meet fellow travellers on hospitality exchange networks: Trustroots
Dumpster diving is possible at least in Santa Cruz. All over the Island you will find lots and lots of fruit trees and plantations. In the right time there are ripe bananas, oranges, medlars, papayas and avocados. What helps a lot is the Chayote. you can find it everywhere and when you cut of the skin you can eat it like zucchini.