What are some examples of foreshadowing in Act I of Romeo and Juliet?

There are two good examples of foreshadowing in Act I of Shakespeare's Romeo and Juliet. The first example occurs in Scene 3 after Romeo has read the list of invited guests for Capulet's party and discovers the name of Rosaline, the girl he loves but does not return his affection. Benvolio has been trying to convince Romeo that he should forget her and look at the other women of Verona. Benvolio says,

At this same...

There are two good examples of foreshadowing in Act I of Shakespeare's Romeo and Juliet. The first example occurs in Scene 3 after Romeo has read the list of invited guests for Capulet's party and discovers the name of Rosaline, the girl he loves but does not return his affection. Benvolio has been trying to convince Romeo that he should forget her and look at the other women of Verona. Benvolio says,

At this same ancient feast of Capulet’s
Sups the fair Rosaline whom thou so loves,
With all the admirèd beauties of Verona.
Go thither, and with unattainted eye
Compare her face with some that I shall show,
And I will make thee think thy swan a crow.

Benvolio is right and foreshadows the meeting of Romeo and Juliet in Scene 5. Once Romeo sees Juliet, he falls in love and forgets all about Rosaline. Like Benvolio, he even calls the other women "crows" after seeing Juliet:

So shows a snowy dove trooping with crows

The best example of foreshadowing, however, comes in Scene 4 as the Montagues are on their way to crash Capulet's party. After Mercutio's Queen Mab monologue, Romeo, in an aside, reveals his fear that going to the party will set in motion events that he cannot control which will ultimately lead to his death. He says,

I fear too early, for my mind misgives
Some consequence yet hanging in the stars
Shall bitterly begin his fearful date
With this night’s revels, and expire the term
Of a despisèd life closed in my breast
By some vile forfeit of untimely death.

As foreshadowed, the "night's revels" lead to his relationship with Juliet and the tragic circumstances of their love. Fate or a "consequence yet hanging in the stars" takes over Romeo's life as catastrophe after catastrophe changes his life forever. The final suicides are indeed untimely as Romeo is a young man in the prime of life and Juliet is only thirteen-years old.