Learn Hardcore Croatian: U torbici mi je ostala još jedna novčanica, ali nemam dovoljno sitnog kusura. - I still have one more banknote in my purse, but I don’t have enough small change.

torbica (dictionary form = nominative singular)
u torbici = locative singular of torbica
If u meant “into” (movement), it would take the accusative: u torbicu (“into the little bag/purse”).

What is torbici exactly—why the -ici ending?

Torbici is the locative singular of torbica (a feminine noun). Many feminine nouns ending in -a form the locative singular with -i:

torbic-a → (u) torbic-i
The extra c you see is part of the stem (torbic-), not added by the case ending.

Why is there a mi in the sentence? Does it mean “me”?

Mi is the dative clitic of ja (“to me”), and in Croatian it’s very commonly used to show possession/affectedness in situations like this—similar to “I have … on me / in my bag”.
So U torbici mi je ostala… is a natural way to say “(In my purse) I have … left”.

Could I also say U torbici je ostala… without mi?

Yes. Dropping mi makes it more neutral and slightly less personal: “In the purse, one banknote remained.”
With mi, it more clearly signals “in my purse / for me”.

Why is the word order U torbici mi je ostala and not Mi je ostala u torbici?

Croatian word order is flexible, but clitics (short unstressed words like mi, je) have strong placement rules: they typically come in the second position of the clause (after the first “chunk”).
Here the first chunk is U torbici, so the clitic cluster follows it: U torbici + mi je + ostala…
Other orders are possible, but you still try to keep mi je in that early clitic position.

Why is it je ostala (feminine) and not je ostao?

Because the past participle agrees in gender and number with the subject. The subject is novčanica (feminine singular), so you get:

novčanica → ostala (feminine singular)
If the subject were masculine, you’d use ostao; neuter: ostalo; plural: ostali/ostale/ostala.

What role does još play in još jedna novčanica?

Još here means “another / one more” (and often also implies “still remaining”).
So još jedna = “one more / another one”.

Why is it jedna novčanica and not jednu novčanicu?

Because jedna novčanica is the subject of the verb ostala (“remained”), so it’s in the nominative.
You’d use jednu novčanicu (accusative) if it were a direct object, e.g. Imam još jednu novčanicu (“I have one more banknote”).

What does novčanica mean, and how is it different from kovanica?

novčanica = a banknote/bill (paper money)
kovanica = a coin
So the sentence contrasts having a banknote left but lacking small coins/change.

In the second half, why is it nemam and not nema?

Because nemam is 1st person singular (“I don’t have”).

nemam = I don’t have
nema = there isn’t / he/she doesn’t have (depending on context)

Why is it dovoljno sitnog kusura—why are sitnog and kusura in the genitive?

Quantifiers like dovoljno (“enough”) typically govern the genitive in Croatian.
So you get:

dovoljno
- GEN → dovoljno kusura
  The adjective must match that case too: sitnog (genitive singular masculine) + kusura (genitive singular).

What exactly is kusur? Is it countable?

Kusur means change (money you get back or small change in general). It’s often treated like a mass noun, so Croatian frequently uses it in singular forms with quantifiers: dovoljno kusura, malo kusura, puno kusura.
You can talk about specific coins too, but kusur itself usually behaves like “change” in English.

What does sitni kusur mean, and why is it sitnog here?

Sitni kusur means small change (literally “small change”).
In your sentence it becomes sitnog because of the genitive required by dovoljno: dovoljno sitnog kusura (“enough small change”).

Is there any difference between sitnog kusura and sitnoga kusura?

Both are correct. sitnog is the more common shorter form in everyday usage. sitnoga is a longer form that can sound slightly more formal or emphatic, but the meaning is the same here.

Could I replace ali with something else?

Yes. Ali is the most common “but”. Alternatives include:

no (often a bit more formal or literary)
međutim (“however”, more formal and usually placed differently)
In this sentence, ali is the most natural choice.