Well let me tell you a little story... I've been doing mentalism more or less full time since the late 1980s and early 90s and for most of that time I've not used Pre-show much at all. This is a deliberate thing on my part in that I loathe it and I'm not comfortable with it. Sure, you can get some wonderful hits via said ruse, but I'm not a magician and my material don't have to have that hard hitting kick of a magic trick.
Yes, I am cheating.... I'm allowing years of experience to work to my favor but I personally believe that most of us put too much stock into pre-show vs. THE show. We look at accomplishing tricks vs. miracles and most important, we don't have enough confidence in ourselves to pull it off so we want the pre-show material as insurance.
My act is what one friend referred to as "Gut Magic"... that is to say, you have to have guts or the balls of a very large elephant to do the kind of material I do in that it is not 100%. Sure, I have that handful of key pieces that are going to hit every time "for entertainment purposes" as they say, but the greater whole of what I do is "real"... that is to say, I tune in and go for it by employing everything from Psychological Controls (forces) to Anagrams and a huge amount of Kenton Knepper's thinking (see the book MIND READING as well as the Wonder Words series).
Yes, I do a Q&A and there are times when I have some advance info on a couple of key people in the room but as a rule I'm not running around with clipboards or doing center tears or all that other silliness you've read about... it's simply not a necessity if you think through what you want to accomplish and why.
The beauty of Mentalism is being able to walk into any room or group of people and on the spot go into your business. That's how reputations are built... and I'm not talking about doing some simple pocket stunts, as it were. Rather, I am talking about doing an act...a real show if need be.
We have a concert hall here in town that I drop in on every once in a while... one night they were have some tech problems and the audience was getting restless. Without being asked I rolled out to the center of the floor nearest the bandstand and just called out the name Jane... I proceeded by describing random things that were popping into my head and finally this young lady stood up and said,
"My cousin's name is Jane and everything you just said has happened to her just recently..."
Well, I continued and as time moved on I shifted from the Readings to Drawing Duplications, Book Tests (using books people present had with them... this town is surrounded by 5 major colleges so books are easy to get) and a few other bits for roughly a half hour. The audience was dumbfounded, the management of the club ingratiated (in that I covered their butts) and my phone rang off the wall for both, Readings and gigs for much of the following month.
I don't go out with a bunch of stuff in my pockets... I don't have any of those nifty wallets or all that other "JUNK" thats out there just knowledge. Which brings us back to your issue; actually study and learn how to do mentalism and strive to do it as clean as you can without the need of all those other things. Then when you are in the position to create a bigger and better program that's of higher profile, you can ring in that kind of material so as to add to production value as well as what I call "jaw dropping power"
BTW... one of the best pre-show guys I've ever watched is Jon Stetson...he's a genuine artist when it comes to such.
