Part of the impromptu definition it says with little or no setup. This "little" could probably be said as impromptu.
Didn't Asher have an effect similar to this in one of his books? Just curious, because if I recall, I believe that you would be able to simply place the card into the bag in performance, thus making it entirely impromptu, provided you had, or could borrow, a bag.
P.s. for me, "impromptu" requires that everything used be un-prepared before hand (preparing under heat is fine) and everything being used is un-gimmicked prior to performance. Again, gimmicking in performance, or using a regular item as an impromptu gimmick is, imo, acceptable.
Just because you always have your ITR on you does not make the floating bill impromptu. Certainly MORE impromptu that usual, but not truly impromptu, imho.
P.P.S. Not that any of this post script matters or is truly relevant to Witness, I guess.
P.P.P.S. Any additional p.s.'s after the initial p.s. (post script) require an additional "P," not an additional "S." As in POST post script, meaning after "post script," or POST post post script, as in this one. An additional "S" would be post script script which doesn't really make any sense. Again, not relevant, just something I was reminded of when adding my p.p.s.'s