Hi Carol, I'll give it a try... money isn't countable. Dollars are (or euros, if we're in France). So it's 'un peu d'argent' and 'quelques euros'.

Same with food--the word bread or milk is uncountable, so it's 'Un peu de pain/lait'. But slices of bread/drops of milk are, so it's 'quelques tranches de pain/gouttes de lait'.

I guess the simple answer would be, if you can substitute 'some' with an actual number, it's quelques. If not, it's un peu. Hope that helps.

I also see now that you asked about quelques vs. peu...if you mean peu instad of un peu, then it's different. Peu is few as in not many/much, and you can use that with countables and uncountables alike.

thank you, countable/uncountable finally makes sense

There's that distinction between countable and uncountable objects in English as well. It determines which adverb to use: few or little, much or many.

On the question of "little" vs. "a little":

Countable objects:
few = peu: j'ai peu d'amis -- I have few friends (meaning not many).
Note: you cannot say j'ai un peu d'amis to mean "I have a few friends". In this case you would use j'ai quelques amis. Un peu is strictly reserved for uncountable objects in French.

Uncountable objects:
a little, a bit of = un peu: j'ai un peu de lait dans le frigo -- I have a little milk in the fridge.
little = peu: j'ai peu de lait dans le frigo -- I have little milk in the fridge.