I could be wrong on this, but i don't believe there are tools included which would help you change the spark plugs. Just enough to help change a tire. If there is anything beyond the lug wrench, it would be just a reversible blade screwdriver and maybe a pliers. It would have been rolled up in a dark red canvas bag.
Another option you have, if you feel the mechanic took it, is to ask for it back, but why a mechanic would be compelled to steal from his customer is beyond me. And if he did steal it, and gives it back, or at least admits to it, i'd find a different mechanic. What sort of mechanic would take the tool kit? What are you supposed to change the tire with, your teeth?