I'd go for a walk, though a bike is also rather nice as well. Walking just involves less things to worry so I can drift off into thought a bit more as I do so.
See the future. Changing the past brings with it a whole host of potential problems (if I make one minor change, what effects will that have on the present?), and I'd rather look ahead to avoid making mistakes in what time I've got yet.
Wrap yourself up in a blanket, or put the heater on?