NO!!!! Don't improvise, be prepared.
Have a three-trick routine practiced and ready to go for situations like this. That way, when someone asks, you have a polished set ready to go instead of freezing up, or a handful of unrelated tricks as you think of them, with no thought about what trick makes a good closer, or opener. When you are left to improvise, the tricks don't come in the order of good opener, strong middle, great closer" - they come in the order you remember them.
The first little set I learned (and still do) is a cut to the aces trick, followed by twisting the aces, then Doc Daley's Last Trick. The tricks themselves aren't important - it's that it's practised, polished, and ready to go anytime. Don't have to wonder about what ones to do, what to say, transitions - it's all done.
Next thing you know, you have a solid routine that will only get better. A couple more mini-sets, and you have an entire show ready to go.