@ratchet freak is correct. The protrusions are canopy poles, where the canopy in the evacuation slide/raft is propped up. The image below shows a canopy propped on them.
Image from tulmar.com
From the document:
The canopy is supported in the center in 4 places by inflatable yellow “CANOPY END SUPPORTS” and “CANOPY CENTER SUPPORTS”, and supported along the sides by 14 numbered supports on the top of the slides inflatable structure.
Here's a closeup of the support from the same document.