No disrespect to Yul (cause he knows I think he's been great for these boards), but it still depends on what you get used to. I've never had a starting clamp, shears, a pathfinder awl, and although I have some snips, I rarely use them (they came in a small set of tools that came with the stringer. I think a 3rd clamp is very handy though. With an Ektelon machine, a half-length slide bar with a 3rd clamp allows you to string an ATW pattern much easier than a starting clamp. For clipping strings, nothing beats a toe-nail clipper in my mind. You can get right up close to the knot, and because of the concave curve in the jaws, it would be awfully tough to accidentally cut the string, and you're also less likely to scratch the racket. Shears?? I guess if I ever HAVE to do 20 rackets in a day, I might consider them--probably not. An awl is essential, but not for moving strings. I haven't used an awl to get through a block hole in 15 or more years (10,000 or so rackets). I have to admit, I did when I first started stringing, but look back at those days and think "boy, was that dumb". There are other, far better ways of getting through a blocked hole. Planning ahead is the best one.
Don't get me wrong. Yul's tools (wow, I like that) are fine if that's what you get used to. But I wouldn't rush out and buy them if you're happy with the things you're using now.