Possible Clues:

• Breakfast noisemakers
• "Snap, Crackle, Pop" cereal
• Cereal with elf mascots
• Cereal brand
• Breakfast brand made into 'treats'
• Re Special K — inspire mix without nuts: Alpen cereal?
• Breakfast brand since 1928 that hints at the starts of 20-, 33- and 43-Across
• Popular baked treat ingredients