(1) At a pinch/push = if absolutely necessary ;  only with a certain degree of difficulty.

• There is room for four people, or five at a pinch.( or push- in this context ‘ room’ means  space).
• We usually accept 55 guests , but at a pinch we could take 60.

(2) Have a bash = to make an attempt to do something.

• I have always wanted to have a bash at writing.
• A : Do you want to try driving my car, to see how you like it?
• B : Yeah ,sure, I’ll have a bash at it.