I have a 2006 Pontiac Torrent with around 39,000 miles. The engine light came on tonight. What could be the problem? Is it safe to adjust the gas cap (if it's a possible issue) and drive around for another day?

Most likely its your downstream o2 sensor oem price roughly 120 then 80 for the install less you do it yourself

The check engine light indicates a problem with one or more of the sensors monitoring the engine. You will need to have someone scan the engine computer for trouble codes to find out what the problem is. If the engine is running ok, there should be no problem with driving it until you can have it scanned. I do not know if the gas cap is part of the problem.