Walmart top soil is ok. 1 dollar per bag. Scotts compost works but is too expensive for that job.
More important is to use a rake. (metal one with thin teeth) rake the lawn expose the soil before seeding, and rake again to mix seeds with the soil after the seeding. If you soil is very dry sandy and hard, add a layer of soil helps. This is the way to thick up the lawn in thin spot.
If the spot is total dead, you have to remove the top dead grass, lose up the soil about 5 cm. seeding and cover the seeds with very thin layer of soil just enough to cover it. Don't leave dead grass there, seeds would not grow on dead grass since it would dry out.