A trash can or trash symbolizes all sorts of things that have no value. It symbolizes useless and dirty junk, probably in a spiritual sense (if the rubbish that you saw in the trash can was old or rotten food, then it symbolizes “words” or “teachings” that have no value at all, etc. It all depends on what is in the trash can.
The opposite can also be true, for instance, if you find something very valuable in the can like an expensive watch that is still working, the trash can, in such a case, may represent a person who misuses or wastes his time because he or she does not understand the value of time. Life is short and time is precious.