I carry a wood handled 4" Repala Fillet Knife. It's light and strong and I've found it to be a great choice for backpacking. I attach it to my waist belt on my backpack so it's easily accessible and never even feel it a bit while hiking.

I used to carry one with a 9" blade when I lived in California and did a lot of salt water fishing. It was a great knife for hiking and camping too, but I found it really intimidated people I'd meet on the trail or in a parking lot at the trailhead. I've had that knife for 31 years and I use it in the kitchen daily now. I've had the 4" knife for about ten, and both have held up better than just about anything else I've bought during those years.

The 4" is only about $15 now so if you've never had one it's a classic knife that worth having. for backpacking I made my own sheath out of nylon webbing.