If the Grinch's suit reflected his transformation, then his bag and sled revealed a entirely different aspect of the holiday season. When you think of a large, Santa-held bag and a roomy, Santa-driven sled, what is one word that comes to mind?
Giving. Plain and simple.
The Grinch's bag and sled represent the actions of taking and giving. The Grinch originally uses these objects to steal from the Whos. He coasts through Who-ville all thief-in-the-night-like and fills his bag and sled with all of their goodies, determined to push them all over the edge of Mt. Crumpit. With that sled and that bag, he's the anti-Santa.
But then, at the very last moment, the bag and sled come to represent the exact opposite of taking away. He uses the sled to roll down Mt. Crumpit and return to Who-ville. And as he empties his bag, he gives back all of the things that he stole from the Whos, single-handedly restoring the holiday tradition of generosity.