For letters, I use various typical office supply letter openers or a cheap paring knife that I also use in the kitchen.
For general use in the house and out and about, I use 1 of 5 SAKs. I also carry 5 cheap folders in each vehicle that I own that are mainly Kershaws or S&Ws. I also have 2 drawers full of over 25 carbon steel and S/S kitchen knives of varying size and quality that were either free because they were inherited from my parents or cheap because I bought them) for kitchen use. And I have 1 Gerber machete for the garden when shears or clippers are not sufficient.
And, I've got simple razor blade box cutters and utility knives scattered around the house to cut up boxes and other things with. I also have a huge supply of safety razor blades and utility knife blade on hand to replace the blades as needed.
These "knives" meet ALL of my ordinary cutting needs so that I do NOT have to "use" any of the knives in my collection for such mundane tasks.