OK. Let's start with the 40 mCi of Americium-241. The dose conversion factor, if you inhale it, is 1.2x10-4Sievert/Bequerel, which is 44.4 rem/mCi. The total dose equivalent, if you inhaled the lot of 40 mCi, is 1776 rem, which is enough to kill you pretty quickly. Anything beyond 600 rem is considered to be guaranteed fatal after 60 days. We are not, however, talking about a huge public health threat. You could poison a few people with it if you didn't dilute it too much and could deliver most of it into their lungs. (Sorry, I couldn't find the ingested dose conversion factors.)
The inhaled dose conversion factor for Cesium-137 is 8.6x10-9 Sv/Bq, which is 3.182x10-3 rem/mCi. The total dose equivalent for 8 mCi is 25 mrem, or about what you typically get in a year's time from cosmic rays.
Translation for the physics-impaired: The amount stolen could be dangerous to a small handful of people if you applied it just right, but basically one bottle of Drain-O would be more of a public health hazard.
And it's not enough to make a radiological bomb out of. Even if someone stole several hundred of these and then scattered their contents evenly over a city, the effects would likely be totally unnoticeable.