I borrowed this from another BB (SE Flyfishing Forum), it makes a good of good points, some of which I have learned the hard way.

Tips for that first paddling adventure

So, you've decided to rent a canoe or kayak from one of our New River outfitters...and give it a try...either just to see if you want to continue to do this and chase smallmouth bass etc thru the summer...or maybe you are thinking about buying something. Here's some helpful guidance before you rent that boat....

A little research on paddling strokes and techniques is a really good idea for canoe or kayaks....as well as a little study on what to do if you capsize. It's all over the internet...or one of the books by Cliff Jacobsen.

Perhaps purchase your own life jacket, that you will wear, and with some pockets for sunscreen, fly box, and other accessories....so you don't have to go crawling and leaning around to reach a tackle bag...twisting and leaning in a watercraft can lead to an unexpected dunking...all dunkings and capsizes are unexpected. It can happen to veteran paddlers. Be prepared!

Anything of value, that needs to stay dry should be in a legitimate waterproof case or dry bag...secured to the boat.. And...make sure your car keys are absolutely 100% secure in a zip pocket or cord around your neck...and have a spare hidden on the car. Yep...seen folks loose their keys and no spare. You know the name of the creek...

A couple of 15-20' sections of 3/8 --1/2 floating rope (poly rope from Lowes or Home Depot....primarily to tie to the boat and to tie around your waist or clip to your belt when you want to get out and stretch, or to wade and fish. Don't want your boat to blow away and drift downstream...yep...seen it happen...not a pretty sight....same creek name...

Put the boat in the water, floating, before you get in...don't try to keep part of it resting on the bank and push off. Getting out...turn the boat sideways to the bank/beach and get out. Don't try to power the boat up onto the sand and rocks... It won't work and it's more unstable. Have the entire boat floating when you get in and out. Have one person hold it stable while the other gets in...then have the person in the boat stablize it with a paddle touching the bottom. Have a hand on each gunnel...and place a foot in the centerline.

If you have read up on anchoring, and you are comfortable with the process, then bring one suitable for a canoe or yak.... If you haven't studied up on anchoring, leave it at home and plan to rest the boat against a rock, ledge, shoal, bush etc to hold it in position when you want to fish a spot. A mesh bag, filled with a few rocks make a decent temporary anchor...and no weight to transport home.

Drifting, floating and catching and landing fish all at the same time is tough...if you hook up (or get hung up) you'll want to stop your drift. Best is to rest the boat against a rock or ledge or shoal to fish an area...or get out and wade...use the rope!
If you plan to wade much...wear good shoes or better still your felt-soled wading boots. Flip flops and sandals usually don't offer much foot protection.

On your first trip or two, keep the gear to a minimum e.g. do you really need a cooler with ice...and that full-sized tackle bag. And if you don't want to chase it downstream, tie it to the boat...more cord or rope

A simple first aid kit with antibiotic cream...and clean water or peroxide to flush a cut. there's some weird stuff living in our waters... I know of at least 2 serious episodes from cuts while paddling...

And maybe a simple folding seat e.g. Crazy Creek chair to supplement a crappy or non-existent seat in a sit on top kayak or strap to a canoe seat for some back support.