"Bagajul meu conține două geamantane mari și unul mic."

Translation: My luggage contains two large suitcases and a small one.

[DavidCarver]

"consists of" rather than "contains" - unless the big suitcase and the small one are inside an even bigger case.

[DaveDerecs]

Yes. "Consists of" or "is comprised of" are both far more natural than "contains".

[hippietrail]

Let me guess: Your suitcases that was inside your luggage contains a backpack, and inside that you have a briefcase, and it is full of babushka dolls?

[mascha53]

What is the difference between ”un mic” and ”unul mic”? wanted to translate the latter as ”one small one” and it was not accepted.

[ovidiu_nl]

"Unul mic" is "one/a small one".

"Un mic [...]" is "one/a small [...]" (you have to name the object).

I think in this situation "one small one" would have been a better translation.

[ChipAgapi]

Ovidiu is right! Actually the word "mic" is polysemantic... If one just says "un mic", it means "a burger" (in Romania "mic" - pl. mici - are very popular small cilindrical minced meat burgers)

Another distinction to be made here:

unu, unul (f. una) - indefinite pronoun

un, o - indefinite article

unu - numeral