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.