I suppose that the provider can use the argument that "I had no idea there was any money in the envelope" defense; but the likelyhood of that standing up to a judge or jury is pretty remote.

Otherwise, we're just saving the provider the cost of finding a way to keep the bills all in order while it's in their handbag.

I've taken to buying cases of envelopes from Staples to cut down on overhead.

(still not a lawyer, not much of a comedian either.)

Not sure about the legal angle....but giving money in an envelope is more classy than just passing on a wad of bills

I bring other stuff with me besides the envelope (a newspaper or magazine, if its during the day my briefcase).  I never mention a word about the donation -- either at the visit or any time beforehand -- and when I come in I set the envelope down immediately, in a very prominent place so there is no way she can miss it.  And then I never ever talk about it.  When I leave I take my other stuff, but leave the envelope behind.  Sometimes the providers mention $$$, but I never do.

Legally, the is really no benefit for the envelope.  a prosecutor could use it as evidence of intent if you were to be charged.

I believe it's mostly a 'classy' thing.  Throwing a wad of cash at a provider isn't very classy.

(disclaimer: not a lawyer)

I've started going by the local card shop and buying a card.  
A blank or genaric message card works fine.  Or if its around some holiday like Chirstmas or St. Partricks Day I'll get one of those.
I think its a little more classy than a plain envelope full of cash.