I guess anything is impromtu if you carry the props.

Check out this thread on the MagicCrape, basically someone asks 'If someone came up to you who knew you did magic and asked you to do a trick, what would you do (impromtu)."

Check out the genius reply by user 'fishsticks', who says "I'd make a rose appear and then do a card trick that really fools them".

I can accept a lot of us carry a deck around, but does fishsticks walk around with a rose concealed on his person?

Anything is impromtu if you got the props with you, but how likely is it?

Personally I'd do Harbin's Zig-Zag illusion because I carry it around with me whereever I go and always have a trained assistant on hand.

MW.