We won't be able to on holiday if/in case/unless we start saving money.
We won't be able to on holiday unless we start saving money.
I'll give you a key in case of/in case/unless I'm not at home.
I'll give you a key in case I'm not at home.
In case/If/In case of an emergency, press the alarm button.
In case of an emergency, press the alarm button.