I've answered previously that a folding saw in combination with a knife is probably the best you could do as far as a good compromise between versatility and weight.
However, if you don't mind adding about a pound to your pack, then a really fun chopping tool to have is a hatchet. In my opinion they are better choppers then any knife their weight, and they are just fun to use. I recommend Wetterling hatchets as 'bang for the buck' champions and Gransfor Bruks if price is no object.