I always take a spare when solo or in a group of two that won't be splitting up at some point. A group intending to stay together for a whole week long trip? One spare might be overkill.

The last tandem trip I did was planned as a three week outing into new territory. Three/four hours from the put-in I heard a crack that sounded bad. Bow paddler's graphite (fairly new) paddle busted at the grip. I offered epoxy - he countered with return policy and our spare. He used the spare for the rest of the trip with good results.

My own paddle is a really old Styrofoam, kevlar, epoxy combo that you don't see any more. It came as a free perk with my canoe. The store personal said no, no, no - that's not the paddle you want for where you are going. Hey, it was the most expensive paddle in the store and the one I thought I could deal with. Still have it, use it and I trust it a whole lot more years later. Still take a spare incase mother nature's waves rip it out of my hands.

Use to go with a guy who would drop his paddle in mid stroke and yell "fish on!" If I were him I'd take two spares on a solo.