To snap yourself back to the present moment (away from thoughts of past or future), ask yourself, "Doesn't this feel good?" The question asks you to ponder where you are right now and whether it feels good or not. It forces you to assess your current now and it also asks you to feel for the answer, not think about it. The question bypasses thought and goes straight to the body.
Even when feeling mildly uncomfortable, like when hungry or tired, this question works quite well at reminding me to be present. It gives me a larger perspective. Imagine you are god (which you are) and you are just now realizing you have a human body (which you do). No matter what you are feeling or experiencing, the moment is a miracle. And if you can hold that greater perspective, every now feels good.
Doesn't this feel good? Doesn't it feel good to have arms and legs and fingers and eyes? Doesn't it feel good to breathe? Doesn't it feel good to wear warm clothes? Doesn't it feel good to hear birds sing? Doesn't it feel good to listen to music? Doesn't it feel good to be in this physical body? Doesn't it feel good to be in the now? Doesn't it feel good to explore the mystery of life?