At a recent paddlesports festival, mention was made of group vs personal first aid kits, the latter being something that is accessible from the cockpit. I do keep a well-stocked first aid kit in the forward compartment and have assumed that for pretty much anywhere I paddle, save for a very infrequent crossing to a barrier island, I’m usually within 30 minutes or so from a laudable shoreline. In terms of what’s immediately accessible, I just have some Ibuprofen and antacid. Although I’ve never needed anything from my first aid kit in nearly 30 years of paddling, I’m trying to think if there’s anything else I really should be able to access immediately from the water. Any thoughts?
Defibulater 
Aspirin
I think what’s more important isn’t what you want access to while on the water. It’s what you want to have on your person if you get separated from the boat. I have a small first aid kit in a watertight container in my PFD pocket. It also contains a few essentials like fire starting equipment, emergency fishing gear. I hope I never have to use it, because it isn’t much. But it’s better than nothing.
Well, the way I think about it the things that I can think of that are most likely to happen while I am on the water, and that I could take care of and then resume paddling without a lot of fuss, are jellyfish stings and sea sickness. So those would be the things I would have accessible to me while paddling.
Other emergencies would require a lot more action and likely would derail the trip, so those things can be in a day hatch behind me.
Aspirin in case I have a heart attack.