A few simple things that make me very happy:
Really good bread.
Really good cheese.
Coldness when I'm sleeping, so I can cuddle under blankets.
Boots that are comfy.
Playing really good, engaging video games.
Making people laugh.
People making me laugh.
Finishing something, and knowing I did it well/my best (a rare occasion).
Scones with cream and jam.
Seeing people I like to be around.
Dressing up in costumes.
Good movies: make you laugh and make you cry.