Its so hard to narrow it down to 'must haves' , SAKs allow such a variety of tools, you can really narrow things down to your personal needs. In my experience, its hard to go wrong so long as you stick with Victorinox or Wenger.
As far as my personal choices, I've had a Vic Classic on my keys as long as I've been carrying keys and spent the better part of 10 years EDCing a Hiker. These days, a single blade folder and the classic tends to be my daily loadout, but if I'm wearing a jacket or coat, theres a pretty good chance I have a Tinker or Pioneer Rancher in there.
As far as my personal choices, I've had a Vic Classic on my keys as long as I've been carrying keys and spent the better part of 10 years EDCing a Hiker. These days, a single blade folder and the classic tends to be my daily loadout, but if I'm wearing a jacket or coat, theres a pretty good chance I have a Tinker or Pioneer Rancher in there.