It is possible to contract rabies through any close contact. There is at least one case of a caver contracting rabies from infected bats while exploring a cave. However, in that case, the caver was exposed to the air in a confined space and probably the fecal matter (guano).
The good news is that rabies is a rare disease, even among wild animals. The reason that everyone freaks out so much about it is that it is hard to diagnose, not curable or preventable once symptoms appear, and is always fatal after many days of horrible symptoms. The fact that your 'possum is eating, and is not seen in the daytime (they are nocturnal animals) is a sign that it is not sick and probably not infected. Wash your hands, wipe off the garage door opener and don't give it a second thought.
-RJ