I personally like to look at pictures of cute things and eat copious amounts of food.
Honestly? Being able to sit at home and do nothing. My weekday life is so busy and almost every weekend is jam packed, so when I am able to finally get some down time, I like to do nothing. I sit on my porch and look at my garden, or I'll take a drive and sit on the beach for a while.
Riding too. Riding my bike is such a great stress reliever as well as very beneficial in so many ways to me that I try get on two wheels as often as I can. An hour or few of helmet time does wonders for me.