Aside from nodding vigorously and shrugging my shoulders a lot, I've found the following phrases extremely useful when trying to blag my way to sounding like an Italian.
1. 'Boh'
Must be said with heavy shrug of shoulders and face like the emoji with the upside down smile (this one 😟). A cracking word/syllable used to convey confusion, doubt, disbelief and incomprehension, but also covers 'who knows', 'who cares' and 'nothing to do with me'.
2. 'Allora'
Theoretically means 'therefore' or 'and so'. Best articulated very slowly mid-conversation. Useful for buying time when you don't know what to say or when you're trying to tie up a conversation. Good to wave hand at same time.
3. 'Urca!'
A sort of charming cross between 'whoops' and 'oh god'. Used in response to situations like dropping something small on toe or burning toast.
4. 'Che Palle'
Literally means 'what a load of balls'! 'This is severely irritating news'. 'Stop being so annoying'. 'What a bloody pain in the arse'. You'd probably say this if you dropped something large on toe.
5. 'Tonto/tonta'
Endearing term for fool or idiot, best accompanied with light slap on back of said fool's head.
6. 'Conosco il miei polli'
'I know what I'm talking about' (literally, I know my chickens). Not used too often but I like to insert it randomly into conversation with a knowing nod.
7. 'Che Schifo'
'That is absolutely revolting'. 'Completely disgusting' For example, if someone puts ketchup on pizza, this is ample reason to shout 'che schifo!' at them.
8. 'Che fico!'
Bloody hell! Thats cool!
9. 'Dai'
Pronounced DIIIIIIIIEEEEE. Means 'come on', 'give over' or 'go on'. Must be drawn out for at least two seconds longer than average syllable. You'd say this to someone who won't give something back to you, but equally if you are trying to get someone to do a shot of sambuca at bar.
10. 'Basta'
Literally 'enough'. Most useful word in Italian language, should be used when someone is piling something onto your plate, when you're buying vegetables at the market or when some hairy bloke won't leave you alone at bar.