Sweets/choc in my son's advent calendar.
I also add notes to tell him how wonderful he is: good at sharing, helps his friends, kind to animals, perserverance in his sport (if he isn't last, he's penultimate, but doesn't lose heart), that type of thing that's specific to him. He has kept all these nots in a little jar and reads them from time to time.
Last year I stole quotes from the twitter account of Thoughts With Dog, eg " I like to leave as much of my hair around the house as possible. it is my confetti, i am a party", and "hello, it's me again, i love you" written in my left hand (i'm right-handed) and signed by our dog. Total plagiarism but my god did DS laugh! I shall do the same this year, inventing some of my own.
I tried putting activities in one year, but we were so blody exhausted with school and work that making biscuits, crafting or even driving round looking at lights was just not going to happen.
He's had two themed calendars as gifts, one Lego one Playmobil, but he was a bit 'meh' about them. Me too, to be honest, so many bits were rubbish or got lost.
He's 10yo.