Was @ Kopitiam, Bukit Panjang Plaza two days back and they only
accept their Kopitiam Prepaid Card for payment and do not accept
cash at all.
The min purchase of each card is $5. And this apply to all
outlets.
I witnessed a few unhappy customers when I was there. There are
some who dropby to get a cup of drink or a fruit and yet they would
need to purchase the card before they could do so.
There are also students who only have $3 to have their meal and now
they simply can't as their parents are not with them and they do
not have enough cash to purchase the card.
As for me, only after I ordered my food then I was told that they
do not accept cash. 
