Something not too big (or your instructors will conficate it) and reasonably cheap (in case you lose it).
I'd say something like a Swiss Army knife (one of the ones with the locking blade) or an Opinel.
I have a nice flat one, excellent for "I can't believe its not butter"
As I have just read your other post and know that you are about to go into training, do yourself a favour and forget about taking lots of "warry" kit with you. The DS won't let you use it and if it is classed as "offensive" (which a nasty pointy knife will be) they'll take it of you anyway and you'll look like a tw*t.
Turn up with the kit on your joining list plus whatever extras the guys from on here recommend that you take with you, NOTHING else. You aren't a soldier yet and you certainly don't need a big fcuk off pointy serrated Rambo commie killing mofo blade to get you through basic.
A much better question in your position would be âIâm just about to go into Basic, what should I take with me?â and then listen and learn
My own personal reccomendation would be one of those Samurai sword things or one of those double ended Klingon jobbies. Either will impress the hell out of your section corporal and plt Sgt and they'll let you stay in bed an extra hour in the morning as you came prepared.
Get yourself down to Millets or better still a back street gun shop, training screws love a chap showing the initiative.
I suggest an eight inch, stainless bowie knife with elongated blood channel and toughened bone splitter for dealing with baddies in armoured jackets or ninjas
When you get off the coach on the square and are greeted by your new team of NCOs prepare yourself with a line of green cam cream under each eye and say 'Ain't got time to bleed, Mofo' then lob a throwing star at the Drill Sgt
On exercise with a 148Bty Bdr in Georgia (US) some years ago. Septic USMC gets out his knife: it looks like something that Conan would use; compass, survival kit, rope belay, saw, gucci sheath, etc,etc. 148 Bdr gets out his commando dagger.
Septic asks "so what can that do?"
Bdr answers: "it kills people"
"Yeah, cool. But what else can it do?"
"No, you do not understand: it just kills people. That is all it is for: killing people"
"Oh my Gaaaawwwwwwd!!! How coool is that?! Can I buy it from you?"
Said Bdr had (for some unknown reason) brought 5 of the daggers (despite admitting to never having any on exercise before). By the end of the exercise he was getting the most gucci of the yank blades (some were bigger than my Wilkinson sword!) plus other kit in exchange. Made an important mental note as a young officer: always see what more savvy NCOs are packing and replicate (but let them do the haggling for you in return for a case of ale). Every ones a winner (and there is one born every minute).
(no, I was never 148 before I get accused of walting it)