I would second the Buck CrossLock. I don't think much about it's pocket clip but a nice lanyard hole would be perfect for the vest anyway. CrossLocks are solid, easy to use and most important durable. I had one for about 8 years and my dad borrowed it for a quick job and never gave it back. Another knife I would recomend is Gerber Gator. It is also a great knife with blade little wider than Crosslock's but handles are made out of rubber like material. It gives you nice grip and it's easy on your hand when blade is used a lot.

Matt