The only knife I've had to field sharpen without using a sharpening stone was an old machete made out of some really terrible steel. I vaguely remember lapping it on some wet concrete, LOL. And it worked!

When I was a serious hiker/camper I always carried a small sharpening stone, despite the fact that I was packing a "rock". These days I think most folks use the diamond sharpeners which look much more lightweight.