I would say that someone who likes knives would enjoy, at a minimum, having one of each of these four basic items:
- folder, swiss army knife or multitool
- small knife
- medium knife
- big knife

Then if you want to be well rounded and branch out a bit add:
- small axe
- large axe
- machete
- small/medium knife
- med/large knife
- pocket saw
- bow saw

Buy quality on those 11 items and you should be set for pretty much any camping/hiking/bushcraft you would want to do.