Believe in yourself, and be true to who you are; it may not always feel like it, but people see and appreciate the real you. As long as you try your hardest and persevere, it doesn't matter whether you're the best at something. It's important to be liked for who you are. Be kind and compassionate. If you want to get to know someone, talk to them.
A couple uses each of "stupid" and "blockhead." Also "dumb" and "slug" (as in "to hit").
Nothing within the movie, but there are tons of tie-in products available (toys, clothes, books, and much more). Also lots of promotional deals with partners from Safeway to Target and more.
The gang celebrates Snoopy's victory over the Red Baron with a round of root beers.