If you can't think of what to write, tough luck; write anyway. If you can think of lots more when you've finished the three pages, don't write it; it'll be that much easier to get going next day. ↗
When I look back over my novels what I find is that when I think I'm finished with a theme, I'm generally not. And usually themes will recur from novel to novel in odd, new guises. ↗
Throughout my career, when I was finished with the drawing for one film I would go up to the story department and help develop sequences. Sometimes these were for scenes that I would animate later on. ↗