After Mrs. Beaver's packed most of the food supplies:
Susan: Should we bring jam?
Peter: Not unless the witch serves toast!
(which then pays off a little later)
Mrs. Beaver: You should have brought a map!
Mr. Beaver: There wasn't room next to the jam!
And also later on:
Peter: (glaring at Mr. Beaver): If he tells us to hurry up one more time, I'm going to turn him into a big, fluffy hat!
When the kids first meet Aslan.
Aslan: Yes, Peter Pevensie, formerly of Finchley. Beaver also tells me you plan on turning him into a hat.
When the children all fall out of the wardrobe and the Professor hands them their ball back.
A blooper of this scene features William (Peter) missing his cue to catch it, resulting in it clocking Skander (Edmund) in the head. The actor playing the Professor proceeds to laugh as Skander complains "Ow...ow..."
All of the bloopers/outtakes.
When Mrs. Beaver is packing food before the group try to flee from the wolves.
Peter: What's she doing?
Mrs. Beaver: Oh, you'll be thanking me later. It's a long journey, and Beaver gets pretty cranky when he's hungry.
Mr. Beaver: I'm cranky now!
In the book, the repeated advice about not getting yourself locked into a wardrobe. It comes up often enough to make you wonder if it's something Lewis' goddaughter, his primary intended audience, made a habit of.
On the commentary
For the filming of the Turkish Delight scene, the prop masters asked the director if he wanted the "fake" candy. He said yes...and they brought a fiberglass and wire piece which couldn't be eaten.
The pottymouth bucket that Georgie (Lucy) carried around. The boys claim she made up curse words and she references an incident (and clarifying "It wasn't you actually, Skander") where someone swore and her head whipped around to force them to pay up.
Skander (the actor who plays Edmund) is mentioned as not being permitted to eat sugar so William (Peter) apparently tricked him into eating sugar glass and is heard unrepentantly declaring "And he actually went and ate silicon."