When it comes down to it, you don't need much beyond a rod to fish from your kayak. You need more than that to do it comfortably and well, but if you already kayak or have a kayak available, it's possible to get yourself set up for kayak fishing!
***Rod Holder – You need something to keep your rods in place. Your boat can flip or your rod can get hung up on a tree. Last thing you want to do is lose your rod and reel combo.
***Kayak Crate/Tackle Boxes -- Kayak crates combine rod holders with an area to store your goods; a great way to outfit a kayak quickly is using one of these! See a cool DIY to make one here: http://www.vingle.net/posts/424986
***Anchors – Stop your boat or you may miss the fish.
Securing your kayak in a specific location is key when fishing and there is no better way to do it than with a small anchor and line. Don't get anything over 3lbs unless you have to. Claw or folding anchors from the store will work, or you can try to make your own: http://www.vingle.net/posts/486548
***Paddle Leash – Don't be up the creek without a paddle: secure it! By installing a simple device that secures your paddle to your boat, you’ll never have to worry about losing a paddle when you catch the “big one”. One end simply ties to a piece of hardware or installed accessory on the boat and the other to your paddle shaft. Leashes are better for fishing from your kayak than the clips that a kayak typically comes with.
Make one for your rod, too: http://www.vingle.net/posts/424992
By getting these basic things ready, you can be yak angling in no time! Get those lines wet, and have a good day on the water.