Dry ice will just sublime (vaporize) to carbon dioxide gas. In other words, if you leave it out at room temperature, it will just disapear. Just be sure to keep it in a well ventilated area to avoid accumulation of carbon dioxide gas and don't seal the dry ice in a container in order to prevent the container from exploding. If the dry ice is at the bottom of a trash can, the trash can will probably be filled with carbon dioxide once the dry ice completely sublimes (carbon dioxide is more dense than air, so it will tend to sink to low points). This should be fine, just don't try to stick your head in the trash can and breath because (in addition to other reasons why you shouldn't stick your head in the trash can) there will be very little oxygen in the trash can.