My boyfriend absolutely hates going to HHN and I always buy a FFP, so I do end up going alone 3-4 nights of the event when i can't drag a friend or two along.
On nights that I feel like going through houses and waiting in lines, my Iphone is my best friend. I make sure it is at full charge before I leave and just browse the web, play games, or listen to podcasts while in line. Sometimes though, I will just strike up a conversation with the people around me which normally makes the lines go by quite a bit faster.
Sometimes when I go alone I don't even feel like doing houses. I will watch all the shows and walk through scarezones multiple time, or sometimes I'll just find a seat and soak in the atmosphere and watch people get scared. I also tend to ride more rides when I'm alone.