Depending on the rivers you choose to run, you may need 2 spare oars, per the river's requirements. If you can find a set of spares, I would run with the full set on multi-days. The perk being, if they don't match your main set, you can do a full switch out if an oar is broken.
My bosses swear by the magic sand mat and children, saying it keeps your tent sand free.
Perhaps the best plan of attack is find a friend who has all the stuff already, and then boom, budget saved for more beer and kids snacks!