Here's an item one doesn't hear about these days, an oil can you fill and deploy with your sea anchor to slowly leak oil onto troubled waters. The oily surface it creates can keep dangerous waves from breaking onto the boat in extreme conditions.
Parachute sea anchors packed in self-deploying bags. Available in various sizes and styles.
These cruisers deploys a Paratech sea anchor in gale force winds a few miles from shore, learning five lessons in the process.
FAQ entry about where to get the pattern to make a sea anchor yourself and when to use it.
A drogue "may be even more critical to raft stability than ballast," and has other purposes according to this report, which looks at various (primarily aircraft) liferafts and how they rig a sea anchor.