Hi ladies! I need some help!

My boyfriend has to take a huge exam for a promotion at his job. I wanted to leave something on his car the night before that he will find when he goes to leave for his test. It's a surprise & he locks his car so it would have to be something that could be places on the outside of the car like on the windshield or something! I was thinking a card to wish him good luck, but what else can I put with the card?!! Thanks for any suggestions!😘💗