extemporize

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To do or perform (something) without prior preparation or practice.
• intransitive verb To perform an act or utter something in an impromptu manner; improvise.

from The Century Dictionary.

• To make or provide for a sudden and unexpected occasion; prepare in haste with the means within one's reach: as, to extemporize a speech or a dinner; to extemporize a couch or a shelter.
• Specifically To compose without premeditation on a special occasion: as, he extemporized a brilliant accompaniment.
• To speak extempore; speak without previous study or preparation; discourse without notes or written draft.
• To sing, or play on an instrument, composing the music as it proceeds; improvise. See improvise.
• Also spelled extemporise.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To speak extempore; especially, to discourse without special preparation; to make an offhand address.
• transitive verb To do, make, or utter extempore or off-hand; to prepare in great haste, under urgent necessity, or with scanty or unsuitable materials

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive To do something, particularly to perform or speak, without prior planning or thought; to act in an impromptu manner; to improvise.
• verb transitive To do, create, improvise, adapt, or devise in an impromptu or spontaneous manner.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb perform without preparation
• verb manage in a makeshift way; do with whatever is at hand