Different kayaks are laid out in a variety of ways.
99% of them are totally hollow. Accessing that area differs on each brand/model. Almost all of them have forward and aft hatch openings. But, those openings are difficult to get to when in the water.
Better models also have an amid-ships hatch. Most guys bring insulated "Fish Bags" which are built like a tapered guitar case. The fish are slipped into the fish bag, and the fish bag is put somewhere inside of the yak. Some are just tied onto the bow area.
Obviously, one cannot keep more than a couple of larger fish like those shown on the video.
I, personally, have never been BTB (Beyond The Breakers). The "surf" off of Galveston Island is mostly small, especially with a North Wind. Getting out past the breakers, and then getting back in can still be tricky.
The main reason that I haven't gone out is that, at my advanced age, I am not positive that I could safely climb back onto the kayak if I turned it over in deep water. I wouldn't want to ruin some other guy's day by having them accompany me all of the way back into shore from two miles out.
Paddling back in while dragging a 60/70 lb yak through the waves would probably do me in permanently.
So, I live my BTB adventures vicariously by watching the videos of those who do it.
rich