You'll need paddles for each paddler on board, of course, but also a spare paddle, tied down. I like to tie my spare down with a couple lengths of thin bungee cord, which is quicker and easier than rope to undo in an emergency. Also as mentioned, tie-down loops epoxied to the lower sides are very useful.
You mentioned a side-mount for a motor. Make sure that is not attached when you run rivers. If it sticks out any distance, the current will catch it sooner or later, and then you are in big, big trouble. Ask me how I know!
Someone mentioned an ensolite pad for the floor. Good idea, even if there's only small pads just in front of each thwart ("seat"). Those will protect your knees, because you will find paddling on your knees much easier on your back and arms than paddling sitting up. Paddling when kneeling also gives more stability, and enables you to apply lots more power when you need it, like in the wind.