I know this is obvious, but I haven't seen it posted, so here goes.

It would seem that the basics of all impromptu magic, would be slight of hand? Once learned would not the practitioner be able to perform wherever and whenever with whatever? I can recall as an exercise traveling trains, and just doing things to passengers for the heck of it. Not only did we have fun, but my skills were tested as to how much I could do with literally nothing. And when I say nothing I mean not even a deck of cards. Latter I developed a small kit I could carry in a fanny pack (yes I carried a fanny pack) with some basic items like a TT, cards, coins, pen and paper, sponge balls, and such, and even though I was "prepared" the magic still looked impromptu. So I guess the trick is looking unprepared, when in actuality I was.

Just my experience. Hope it helps?

Nice post.

I have a site I call IMP for some impromptu and apparently impromptu tricks.

The link is below my signature.

Thanks Jaz. I've bookmarked your site.

Yes, Jaz, nice site. Well researched and some great resources. Very useful.

Just about every magician I know has some rubber bands either around their wrist or elsewhere & are ready to do some impromptu with them.

Sir Richard.

Buy Martin Gardner's Encyclopedia of Impromptu Tricks.

Yeah I always carry a Card Deck, Loops, Thumbtip and Sponge Balls

"Nothing"
NO Pre-Show Work
NO Stooges
NO Clipboards
NO Nailwriters
NO Playing Cards
NO ESP Cards
NO Billets
NO Wallets
NO Gaffs
NO Gimmicks
NO Special Materials
NO Muscle Reading
NO Hypnotism
NO Threads
NO Mirrors
NO Electronics
NO Rough & Smooth
NO Gilbreath Principle
NO Filler

Intaeresting! Only one is still an active "member" since the OP.

Well Dick, to be fair, at least one is deceased....

A few basic sleights and some creative thinking will set you up nicely. The Magic Book by Harry Lorayne is a great primer for this kind of magic, and if you can locate it, be sure to check out Lifesavers by Michael Weber - these two books are must haves as far as I am concerned.

"Only someone who is well prepared has the opportunity to improvise" - Ingmar Bergman

This is well worth repeating and considering as to this string, and as to the magic of life itself.

New discoveries of neuroscience as to how our brains function (and don't) increases the importance of psychological ploys in performance magic
and certainly impromptu performance before an unknown audience as to experience and appreciation of live effects.

This is why I have changed my approach to describing magic effects in ebooks to include details of "why and when" as well as "how and what,"

plus a "prelude" approach in which you a can evaluate or train the audience as to what good magic is and even branch to alternative effects.

So, in answer to the OP -- the basic to all impromptu is learning what the audience of the moment expects and then give them a bit more.