Have science tradebooks, chapter books, science biograhies available for reading.
During PE, have students monitor their heart and breathing rates, how fast they can run, how far, etc. and then reserach it in health or science class, if possible.
During arts/crafts students could research the materials they are using, the colors in their paints, etc. Pigmentation is every where so even talking about the color in the classroom, their clothing, etc. introduces chemistry.
Current events often include science items, but another class starter is the weather for the day, for the week, etc. and have students give the weather forecast as the year proceeds. This can also provide discussions of preparing for possible weather-hot, cold, storms, etc. and teaches seasons, water cycle, etc.
Just a few ideas.