Interpretations

My first though is that there is some sort of competition going on (hence the boats from sailing team) and it is very dangerous, but you haven't yet acknowledged that danger (like Harry Potter in book 4). Also, you see that there are problems (like dead bodies under boats), but rather than doing something to fix them, you let others do stuff, while you just do what you're used to. I don't know who Henry is, so I can't help you there. Also, these are 'darker' thoughts, so it's nightime.
Then we have your sister. You love your sister, and are around her a lot, so of course she'll show up in your dreams. That you our flying up high in the glider signifies how happy you are when she is around. The lines signify something (or someone) that is holding you back mentally. It may be your parents, since it's at home. Or, it could be your worried that that house sitting lady will keep you from doing something, or it could be your dog (hence the leashes). Also, the bizarre exercise machine part reminds me of those unelectric treadmills in China.
Actually, I just realized that by glider, you may mean bench or something, because your families speech patterns are different than mine. The jewelry is meant to signify romantic interest, and you aren't sure why or if you have is, and, regardless, you want to get rid of it. The tackle-box shows that the jewelry came with friendship (fishing is outdoorsie, and you associate friendship with that sort of thing), and because you were able to give the jewelry back and keep the tackle-box, you have been able to maintain your friendship despite some initial awkwardness. However, it hasn't totally left your mind, hence the valentines. I'm a stand-in for you, here, where you think that any romantic intentions are a sign of desperation. Also, because Lysander is (ahem) unexperienced, his valentine is like that of a child. However, it's still interesting and unique (every page is different)
Us gossiping about guys is because that is what we do. We did it last week, and I'm sure it'll happen again. Guys are just so interesting to talk about. Did dream me have any good gossip?
I'd already told you about having first day of school dreams, and you probably do think about the first day of school a little bit (at least subconsciously). The not knowing which room appears to be a common theme, since I've had that too. And THAT'S MY PHYSICS CLASS. WHY DID YOUR DREAM SELF NOT JUST GO TO CLASS WITH ME???? You worried that your desire to be prompt and do well in school will interfere with your ability to be a good person. You also think you might miss a chance to help if you don't think it all the way through. I associate trains with the school year, but I don't know if you do. This also sounds a lot like the train in the third Harry Potter video game. You're jealous of Tawny and Benny, but in the end, you know Tawny, and you know it won't be problem.

love, tea