For a long time I just carried a Victorinox Classic. Hey, Ray Jardine says it's all you'll ever need! Knife, scissors, screw driver, tweezers, nail file and tooth pick and you can pick them up cheap on ebay. I've bought them by the dozen and given them away as gifts.
Then one day a backpacker, carrying a pack that approached 50% of her body weight, attempted to cross a flooded stream in my own stomping grounds, was swept down river trapped beneath her heavy pack and drowned. I got to thinking: Suppose i'd been there, what could I have done to help? I don't think one person alone could have pulled her and her heavy pack out with the strong current pushing against her. You'd need to slice through the waist band, sternum strap and maybe the shoulder straps pronto. I didn't think my little Classic would be up to it and I started looking for an alternative.
I finally settled on a fixed blade Mora knife with a plastic handle. Number 511 on this website:
It is not nearly as light as some of the alternatives. I haven't weighed it, but the website lists it as 3.5 oz with the plastic sheath. I'm pretty sure you could save an ounce at least with a home made sheath, but it is still a pretty substanial weight investment. I've taken it with me on a couple of trips, but still haven't decided if it is a permanent fixture in my kit.
The only downside I can see is the weight. The knife is sharp and easily sharpened. With the fixed blade and plastic handle, it is nearly indestructible. I can use it as a hatchet by hitting the thick side of the blade with a piece of green wood. It can perform many tasks instantly that would take much longer with a smaller blade and the hilt guard makes it safer to use.
I like carrying the knife because it seems, at least, like a tool I could use effectively in many situations, but realistically, I haven't actually yet used it for anything my little Classic couldn't have easily accomplished as well and I haven't really identified any other items I could leave at home because I'm carrying this excellent knife. The jury's still out.