"Patience, love," he said as she closed her eyes, "this shouldn't take more'n a minute." After waving his hand in front of her face to make sure she wasn't peeking, he sprang into action. He dug around in his robes finding a small parcel that he'd made even smaller with a shrinking spell. Taking it out and enlarging it, he started removing items from it.
He set a chocolate cupcake on a nearby bench and then pulled out a handful of miniature fireworks he'd purchased last summer from the Wheezes. They were supposed to pack all the punch of normal fireworks but in an unobtrusive size - for "special celebrations in crowded places" the box had said - and he hoped they lived up to that promise. They'd come so far, he didn't want to be interrupted now. He placed a candle on the cupcake, lit it, and patted his pocket in search of the one remaining element of his surprise, wanting to make sure it was still there.
Stepping up behind her, he turned her in the direction of the bench, so that she'd see the cupcake when she opened her eyes. "Alright lass," he leaned in and whispered in her ear, "y'can look now."