This is a very n00b question, but to heck with embarrassment. Last year, we purchased two Tarpon120s and love them. But… we were surprised that when stashing gear IN the boat (not on top), that… it’s just one big ol’ compartment in there, so things slide around. The water bottle you put between your legs in the hatch quickly ends up… at either end.
I’m left wondering how this is useful – surely I’m clueless and missing something obvious. 
Put the stuff in dry bags or
put in air bags, aka float bags.
And add air, though that is easier in dry bags.
Between the two you can make stuff stay put. I find the noise of gear bouncing around to be bothersome.
Also experiment
with the fat, long pool noodles. Inexpensive and can be cut to size.
And on the water bottle…
Get a hydrator that you can attach to your PFD, assuming you are using one, with a tube and a mouth piece similar to what bicyclists use. It is a lot easier than a bottle in a kayak.
agree
– Last Updated: Mar-18-15 12:52 PM EST –
I agree with comments above (pool noodles, float bags, etc.)
Also, hydration packs are good (I use one). But bottles can work fine also. But best to not put the one you are drinking from in the hatch. With the entire inside accessible through the hatch openings, if water splashes in while you are accessing your water bottle, could be trouble. Worse yet if you flip and lots of water gets in.
Instead, get a bottle with carabeener on it and attach to your bungees outside the hatch. Or use a hydration pack.
Coozies with a clip.
For water bottles I just use a neoprene insulator (a coozie) with a drawstring closure and a plastic clip on the side that I can clip to any deck rigging in front of me. I think I paid less than $10 each for a couple on Amazon.
They do tend to be on the small side, so a hydration pack is a better idea if you want to take a lot of water with you, but the coozies are inexpensive and work well.
Tethers
Awesome, thanks!
Thanks guys, I learned a number of things from the great responses!
yep
I use a small carabiner, my water bottle has a loop.
I’d be afraid to keep my water bottle in my day hatch but only because of the sanitary conditions…
For other gear
storage inside the hull, glue a couple of D rings inside where you can reach them easily. Put stuff in dry bags and use a mini carabiner to clip them to the D ring(s).
you should be able to find
a drop-in gear bag like this one… may be different size depending on the model year.
http://www.austinkayak.com/products/469/Wilderness-Systems-Tarpon-Kayak-Cat-Hatch-Bag.html