I have such a hard time answering this, and still can't. I'm gonna think some more.
Hey lilstar, it doesn't have to be anything, massive, deep or profound.... perhaps you are thinking too hard.
Other things that keep me going are plans for the future, usually the near future..... planning an evening out with friends, arranging to see family, walking with my friends dog, planning a holiday, or just daydreaming about where I'd like to go.
Also things that I enjoy -ok - they might not 'keep me going' per se, but they are worth thinking about when you are feeling down. For me, it's the sight and smell and sound of the sea, an ice cold beer on a hot day, feeling the sun on my face, coming in from a cold wet day and having a long, hot shower, feeling sand between my toes, curling up in bed with a good book, while the rain hammers on the windows, playing my favourite songs at full blast (sorry neighbours!). Sometimes it's just the simple things that can bring a smile to your face :)