- This is the first day of all my tomorrows!
- Good grief.
- This is it!

4 seconds sound clip from the Play It Again, Charlie Brown movie soundboard.

You can hear this line at 00:15:01.194 in the DVD version of the movie.

Quote context

[...]

- Just leave everything to me, Lucille.

- You tell your lover boy that it's all set. It'll be his first big break.

- See you, Sally. See you, Lucille.

- I've got to tell Schroeder.

- This is the start of my whole future. This is the start of something big!

- This is the first day of all my tomorrows!

- Good grief.

- This is it!

- Guess what.

- What?

- What would you think of a person if that person could do a great favor for another person?

- I would think he was a very nice person.

- What would you think if I could have you perform your old Beethoven in front of a huge audience?

- What do you mean?

- I, your loyal and faithful companion, have arranged for your first recital.

[...]