So many - I had an almost abnormally happy childhood. Thinking about it, though, most of these will sound hopelessly geeky:
Family dinner - every night. After dinner my dad would make us do really long sums to see if we could keep up (5+6+23-16 and so on for ages) but always ended with x0, which would make me so mad! He also used to bounce me on his knee and sing songs he made up until I was laughing so much I pissed myself on his leg couldn't breathe.
Singing in the car on long journeys with my mum and brother. We used to do whole musicals from beginning to end. I still know all the words to Joseph and the Amazing Technicolor Dreamcoat and West Side Story.
Playing scientists with my brother and best friends - we used to take the middle spongy bit out of felt tip pens and run them under the tap to create different colours of water which were of course secret potions. The game then turned into spies where we would try to assassinate each other to get the potions.
Playing on our old swing frame when we go too old for the swing. We had three planks, two massive blankets, a basket of pegs and quite a lot of rope, so we used to put the planks over the crossbar of the swing, peg the blankets over it and make the tiny city garden version of a treehouse, then use the ropes to create a pulley system so that mum could put food in the basket from the kitchen window and we could pull it into the den.
Mum let us play with what she was cooking, so when she bought whole mackerel and cut off the heads we put the heads on the kitchen taps so water came out of their mouths, and when she was trying to cook pigs feet and pea soup for my dad (disgusting treat from his childhood, wasn't nice) we were allowed to pull the tendons in the trotters with pliers to make the feet move.
Making Christmas cake during October half term, with a tiny glass of sherry and Meatloaf on the record player.
Oh God, have written loads, and looking back, no wonder I am was such a spod.