1. Known as number one
2. Found on the edge of Trinidad and Denmark
3. Tool for filling six pockets

What's missing?

Hint 1:

Alone, I am considered worthless, but together with my brothers and sisters, we can be a small fortune.

Hint 2:

I'm kept safely in objects of all shapes and sizes, but my most commonly known home is inside the belly of an animal.

• A bit of feedback: I think the original puzzle was far too underclued, especially since there's no way of knowing if you had gotten 1 of them wrong. – Sp3000 May 12 '17 at 2:48

We know, based on humn's answer that:

The letters are P,D,Q

And from the hint that:

Together they are worth a small fortune

So what is missing is:

N for nickel. The letters stand for Penny Dime, Quarter, Nickel, a small fortune.

Edit, finally figured out the last clue, LOL.

Piggy bank. Nice one.

$\small\color{black}{\textsf{1. Known as number one}}$
P“pee”/urine, often referred to as “number one” in families with young children.

$\small\color{black}{\textsf{2. Found on the edge of Trinidad and Denmark}}$
D – At the trailing edge of “ Trinidad ” and the leading edge of “Denmark.”

$\small\color{black}{\textsf{3. Tool for filling six pockets}}$
Qpool (pocket billiards) “cue” stick.

$\color{black}{\textsf{4.}}$ $\textsf{Funniest classical composer never}$
Bach = P.D.Q. Bach (alter ego of Peter Shickele), the least real and most hilarious musical offering (21st child) of J.S. Bach.
P.D.Q. Bach’s oddly canted Six Contrary DancesYOUTUBE, for instance, puzzled musicologists and enigmatologists alike, until metrologists determined that his peg leg was three full inches shorter than his natural leg.

This puzzle’s title, Clink Clank Clunk, would refer to...

...silly sound effects used in many of P.D.Q. Bach’s compositions.

• This sounds so hilarious to me. I'm looking forward to playing this.... for friends. Good answer and question. – John May 10 '17 at 23:56
• +1 for 1,2,3 correct, the answer is incorrect, although that Bach piece is hilarious. There's no outside research that needs to be done for this solution - the answer is common knowledge. I'll put a hint in the question. and yes, the title does give a hint as well – indubitablee May 11 '17 at 14:00

Known as number one

I (roman numeral)

Found on the edge of Trinidad and Denmark

Tool for filling six pockets

Q (Cue from Pool)

Potentially leaving

P, for the IDQP?

• +1, #2 and #3 are correct, and you have the correct train of thought in solving the puzzle, but #1 and the answer are incorrect – indubitablee May 10 '17 at 21:35

Known as number one

Letter A?

#2 and #3 have already been found, which gives us