You can place another spell upon your person so that it comes into effect under some condition you dictate when casting contingency. The contingency spell and the companion spell are cast at the same time. The 10-minute casting time is the minimum total for both castings; if the companion spell has a casting time longer than 10 minutes, use that instead. You must pay any costs associated with the companion spell when you cast contingency.
The spell to be brought into effect by the contingency must be one that affects your person and be of a spell level no higher than one-third your caster level (rounded down, maximum 6th level).
The conditions needed to bring the spell into effect must be clear, although they can be general. In all cases, the contingency immediately brings into effect the companion spell, the latter being "cast" instantaneously when the prescribed circumstances occur. If complicated or convoluted conditions are prescribed, the whole spell combination (contingency and the companion magic) may fail when triggered. The companion spell occurs based solely on the stated conditions, regardless of whether you want it to.
You can use only one contingency spell at a time; if a second is cast, the first one (if still active) is dispelled.