How do I find what these breakers go to?
Short of buying and using a tracer, I'd check for:


appliances that were converted to another fuel source
appliances that you aren't using currently (e.g. AC or sprinkler system in the winter)
appliances that you may not notice aren't working, like sump pumps and radon fans
check outdoors, detached structures, in crawl spaces, and attics that you may have missed when labeling the circuits
check for outlets that may have been used to connect a generator


Lastly, if you turned off just these circuits to see what stopped working, do the reverse. Turn everything else off except the one circuit. It's entirely possible that someone bridged two circuits together somewhere.

The location in the panel may give you a clue. Similar appliances are often grouped near each other, and additions tend to be added to empty spaces at the bottom.