In reply to veteye:
I go there on business about 6 times a year so always have a bag of HUFs left over. I just get the cash out of the local ATMs if I need it.
I've paid taxis in Euros before although they were accepted rather grudgingly, but they have Uber now.
Cards are accepted pretty much everywhere so I would just grab a few HUFs out of a machine for cups of coffee and the odd beer and use cards for everything else.
Enjoy, its a lovely city IMHO.