Potty training rewards

We're working on the potty training with Big Dub, and it is progressing slowly. He gets a different reward for going in the toilet at each of his frequently-visited houses (ours, Ba/Om Noi (?), Mimi/Papa (M&Ms)). At our house he gets a SURPRISE which he has come to expect every time he goes #2 in the pot. At first, I had actual surprises, and when I ran out, I made things up, but last night William declared a pair of Eleanor's 9-month pajamas to be his surprise for a successful toilet sit. There wasn't any space left for his double diaper once he squeezed himself into the outfit, so he couldn't sleep in it.