Can I bring something? What do you need?
'Portare' = por-TA-re. 'Serve' = SER-ve, stress on first syllable.
Use this when you are invited to someone's home. Asking what to bring rather than just bringing something random shows thoughtfulness. Italians deeply appreciate this offer — arriving empty-handed ('a mani vuote') is considered impolite.
'Servire' in 'cosa ti serve?' means 'to need' (literally 'what serves you?'). This use of 'servire' for need is very common in Italian: 'mi serve aiuto' (I need help), 'non mi serve' (I don't need it). It is different from 'avere bisogno di'.
Porto una bottiglia di vino, va bene?
I will bring a bottle of wine, is that OK?
Wine is the most classic Italian party contribution
Faccio io il dolce, se vuoi.
I will make the dessert, if you like.
Offering to contribute a homemade dish — very appreciated
Hai bisogno di aiuto per preparare?
Do you need help to prepare?
Offering practical help beyond just bringing something
Bringing wine, flowers, or a cake ('torta') as a host gift is standard Italian party etiquette. Flowers should avoid chrysanthemums (associated with funerals in Italy) and odd numbers (except thirteen, considered lucky). A bottle of regional wine from your hometown is always a particularly thoughtful gift.