Watch TV in my underwear. Obviously.
I don't need to be home along to run around in my underwear :D I am shameless!
Catch up on the tv shows that no one else will watch with me.
Watch kids shows without being judged by family members.
set up traps for burglars. duuuh
....you know damn well what I like to do when I'm home alone.
Video games (or movies sometimes), my headphones cranked and forgetting about the world. But it's SUPER rare that I'm home alone anymore (wife and kids are usually home with me).