Well, naps are a favourite. I go find out where my fluffy cat is napping, and take a nap next to him.
If I decide to stay awake and be bored, I usually default to either watching movies/tv-series, playing videogames, reading books or taking walks. If I get criminally bored, and do not have access to any of the above mentioned, I might get crazy enough to try watching daytime tv in the quest of finding something worth watching. A quest that is mostly futile.