Playing around in the editor
https://www.youtube.com/watch?v=xazjmW9TylA
I was messing about with explosives earlier, the Propane Tank Floats so I wondered if I could do something like what Razor Tail and Liam used to do in Far Cry 2 - a quick effort had the propane tank raising in water then when it gets to the top of the water layer the angled piece has it push away from the water abd drop, it then rolls back into the water and repeats.
It is possible to plant C4 or a Mine onto these propane tanks so you could spend some time and make some crazy things that would give options for killing the enemy.
The Red explosive barrel sinks but you could create something fun that would work if you play around enough.
https://www.youtube.com/watch?v=OOOQUDcg5g0
The BT Bell Physic01
This item falls the second the map starts, if it lands in water it will float and you can jump onto it and float - if you move around a little you can even float on this bell and travel accross water - you can jump from bell to bell also.
I had no luck trying to throw C4 into it, the C4 just rolled off but I imagine you could place a mine or C4 onto it then push the bell into water, the bell is also useful to push around on land so you could use this item for some obstacles / puzzles in an escape map.
https://www.youtube.com/watch?v=KytBlaIlR-0
Just a short vid showing some of the Destructible Items in FC4 (I am sure there are others I missed - and there are some which say Destructible but they don't work unfortunately)
Thanks to Jaavaa who pointed out that the Top & Mid Section Towers are destructible.:)