Have seen many comments about “warming up” a whistle prior to playing and while that makes sense to this newbie … my question is .. how do u do it in a quiet location where people are talking/eating/etc.?? Do you go outside and play awhile or what? Believe it or not … this is a serious question .. really … no kidding. 
Jim
you could put the whistle next to your thigh and leave it there for a while, but you can also blow into the bell-end of the whistle and cover all the holes, that’ll warm it up fairly quickly.
best, amar.
Cover the soundhole and blow through it.
Completely enclosing as much of the whistle in your hands, especially around the mouthpiece end, helps quite a bit and is fairly fast to warm it up. Having a bit of hot tea and then blowing through the whistle with the airway covered will help too! I prefer honey in my tea. I think my brass Gen is indifferent to it though. 
Ailin
http://www.lileks.com/institute/gallery/10PM/3.html
Look at the lowwer right hand corner of the picture.
Arn’t those whistles being warmed?
(look on ebay, and see that there WERE oscar myer wiener whistles at one time)
Saaaay…Are those the new yellow acorn whistles or are you just glad to see me?
http://www.lileks.com/institute/gallery/bananas/4.html
haha…you know what i’m thinking now vomitb.
I went to a session in NY… I won’t say which one. After a while of sitting and watching - I felt like joining in. I thought there was a place… when I tried to sit down someone said… thats only for musicians!
“No - I’m NOT that pleased to see you, this is a whistle in my pocket” was all I could reply. Seemed to work!
You could also put it under your arm (make sure you use a good deordorant). The armpit is always the warmest part of your body. 
ehhmm…it is…? :roll:
Or you could buy the new Acme Whistle Warmer, from Wiley C. Industries. It works like one of those hot dog cookers with the rollers. You plug it in with the optional 1,000 foot extension cord and set it next to your seat at the session.
Only $299.99
Don’t warm the whistle with your breath: that only makes the problem worse. You are trying to avoid putting moist warm breath into a cold whistle which produces condensation.
Instead, warm the whistle dryly by holding the head in your cupped hands, putting it under your arm, or carrying it around in your pocket for a while (watch out for keys and other metal objects)
How about the Jon-E hand warmer?
http://www.preparedness.com/jonhanwarac.html
Combine it with one of these:
http://www.bizrate.com/buy/products__att373813--362238-,cat_id--12060200.html
So what do guys do in concert, when they change whistles mid-set? A warmed-up whistle doesn’t stay warm for long.
Usually in session I play a single whistle (or flute) through a set of tunes.
I’ve never had a situation where I switched in mid-set.
–James
I warm 'em up by sticking them under my shirt.
I saw Lunasa live in Cleveland and they would switch whistles all the time. Kevin would play, say, a flute for the first tune in a set, then he’d switch to whistle for the second tune, or vice versa. Some of the whistle were metal too. Or Sean would play fiddle for the first tune then whistle for the second or third.
Lunasa/Flook plays all those whistle’s in mid -set because as Professional performers they know what it’s like to depend on a whistle to come through for you. There’s really no time for warming the whistle.
Which means that they have whistles that they trust because they have selected and sampled the one’s that can be used for performance purposes! There is a difference. Some whistles really do respond well (less clogging) even though the environment at times may work against you.-Talbert
Although I’m not a Professional, I’d say that there’s no need really to switch instrument in a session, they do it in concert 'cause they want to give a show, and throw in as much variations as they can, but in a session you’d appear a little “over excited” if you did that.