I plan on asking my teachers for recommendations later this week. This gives them over a month to complete the essay and makes sure they aren’t swamped with kids asking (most kids here wait till October or even later). I know I need to include a brag-sheet to help them know what I’ve accomplished outside of the classroom, but I’m not sure exactly what to include on it. Is it basically my extra-curricular accomplishments, or is there something else I should mention?
Generally it’s your grades/test scores, academic awards, extracurricular activities (and awards associated with it), any volunteer work you did, summer programs etc.
However, don’t have the teacher focus on these things on the rec as they are visible in other parts of the application. Have them focus on your other qualities (thirst for knowledge, leadership in the classroom idk stuff like that). It is an opportunity to showcase any other qualities you had, not talk about stuff that you already went over in the application.
My son’s school has a form the students fill out to give their teachers. The form asks questions such as how did you contribute in class, what did you take away from the class, and why did you enjoy this particular class. The teacher references are academic references, so how you performed In the class is important.
First ask the teachers. If they agree to write the recommendation ask what if any additional information they would like you to provide them.
My daughter simply gave her teachers a three-page resume with details of all in-school and out-of-school activities, honors and awards. However, some high schools ask for very specific information in a “brag sheet” and want that in addition to a resume or instead of one. If you search “brag sheet” on Google you will find many templates and guidelines that other schools have posted. You can also search “brag sheet example” and click on images to see samples of brag sheets.
Here is a prior article on CC with some more information:
http://www.collegeconfidential.com/a-brag-sheet-to-brag-about/
The GC at my D’s school ask parents to write the brag sheet. They said some students are too shy to talk about their achievement while parents have no problem in bragging about it. 
At my school we have teacher rec questionnaires that we have to fill out. It had more general questions (what were your grades in my class, how many years did you have me) and then more specific ones (what was your favorite project from my class, where do you see yourself in ten years, is there anything in particular you want me to mention). In addition to that we provided a resume with our ECs, community service, awards, etc.
I agree with everyone above that the teacher rec letters should be focused on you in the classroom! If you feel that you are a leader in the classroom, don’t be afraid to ask your teacher to include that. The college process feels so weird at times because most people aren’t comfortable about “bragging” ! You don’t need too much extracurricular info (unless it involves the teacher) on your bragsheet, a brief summary should be fine. The most important thing is that the teachers speak about you as a student.
Good luck 