Biodegradable adhesives When I travel, I like to walk around, collect some natural objects (shells, coconuts, leafs, etc.) and put them together to produce some kind of "sculpture". I always have in mind that the object should be as much biodegradable and natural as possible. So, to stick stuff together I use some wax (it has also the big advantage that candles can be found more or less everywhere). However, it is difficult to get a neat result because 1) it isn't very strong and 2) it's hard to canalize.

What are alternative adhesives for such projects?

Some examples made in India:
Taking "India" into account, you could surely find jackfruit or mango tree. I would suggest you could use the white sticky latex of jackfruit/ green mango. While eating, I find extreme difficulty in removing the gum like plant excreta from hands,  I am sure it would work as a mantra as far as natural gum is concerned. 

Secondly, in Indian villages you could see loads of mud house decorated with cow dung. Natives throw the just released cow dung to the mud wall even half roasted bricks wall to dry them. So that later on, they could easily take it from there, break it and use it as fuel. As it has a sticky power, I believe it could easily stick with something. If you're joining two halves of coconut shell, use the just released cow dung and symmetrically spread it over the edge. Then simply put the other one over that and let it rest. It will work as a very natural adhesive.