No. 5: Summer as 'school'
Nature is peaking, so take advantage by getting outside to observe the natural world.
Yeah, it's not your usual book and exam format, but that's why it's valuable. It provides a context that helps facts and ideas stick -- whether it's something you covered in class or something new.
Go out and discover some shale and limestone talked about in geology; learn about heredity and genes through the crops and livestock at a farm; take in the clockwork of an ecosystem at a nature reserve; heck, do some calculations about the physics of roller coasters.
Go see how all that stuff you learned actually applies to real life. The best part is that none of this is an assignment but driven by your own passions.
How about some real-world sociology?