A broken brake lever would have a big effect on the trip but it would be possible to keep riding (slowly). A broken clutch lever would be a showstopper. Levers are quite vulnerable and easily broken in a fall.
Rather than carry spare levers, I replaced the stock items with aftermarket folding levers. The idea is that they fold up rather than snap in the event of an unplanned dismount manoeuvre.
As a bonus, these levers are adjustable over a wide range, so they are more comfortable too.