Make no mistake about it, riffing is fundamental.
To show that adage rather than tell - and continue the thread about Paul Westerberg from the last posting - here's some concert footage from a very early version of The Replacements, playing possibly the fastest, most frenzied cover of Chuck Berry's Maybelline ever. With the full understanding that Chuck Berry very likely improvised his own clever lyrics on the bandstand on many occasions, enjoy this example of extemporaneous verses: the best I've seen from the punk era other than James Chance making up entire songs on the spot with the punk-funk-r&b (spiced with 1960's free jazz) bands The Contortions and James White & The Blacks.
Transitioning madly from old school garage punk rock to the loungiest of swingin' sounds from The Ultra-Lounge, check out the great Bobby Darin. Ever the consummate entertainer, Bobby manages to get laughs, fire up the band, make up verses and knock his signature song out of the park.
Then again, also from the early 70's, I can't help thinking of another consummate entertainer, James Brown. In the original 45 RPM single version of "Make It Funky", James riffs about food, shouting "TURNIPS!" "GREENS!" "HOT CORNBREAD!" as the song closes. While I have yet to find said riffing in any live version of "Make It Funky", this presents as good an excuse as any to post a clip of prime early 70's Godfather Of Soul goodness.