Je valt met je neus in de boter!

[lit: You fall with your nose into the butter]
You came exactly at the right moment!

Hij kan nog geen deuk in een pakje boter slaan

[He can not even hit a dent in a piece of butter]
He is very weak, he has no strength

Ze willen graag boter bij de vis!

[They would like to have butter with the fish]
They wish you pay at the time of purchase

Butter is – like cheese- a very important dairy product in The Netherlands.
In the old days the Frisian farmers produced butter from milk first. Then they made cheese from the rest of the milk.
Especially in the Dutch province Zuid-Holland farmers near Leiden and Delft produced a lot of butter.
Like cheese, butter was brought to the market place by the farmers themselves. It was stored in small wooden barrels for transport.