After an interesting low level excursion in a ravine off the end of a runway while building airspeed (yes -- I had scraped all the frost between the rivet lines) I took to carrying a couple extra containers of windshield washer fluid along with a windshield sponge/squeegee.
No way would I dream of flying without a clean wing.
Exceptions can be made for frost over/under wing tanks where approved by manufacturer.