People used to find big bargains at a “fire sale,” a term first applied to discounted fire-damaged goods. You may still find these, but the term now more often applies to financially troubled sellers trying to raise money quickly with very low prices.
When apprenticeships in trades were more common, a new and unskilled apprentice might be asked to hold a candle for light while his master worked his craft. Only a very useless apprentice “can’t hold a candle to” his master’s work and perform even this menial task, and the term also indicates a great disparity between the abilities of the two. A 16th-century writer who was among the first to use the term wrote that he was not worthy to hold a candle to Aristotle.
Working on a project late into the night? You probably have the electric lights on, but in centuries past it would have been an oil lamp lighting your work. This is the origin of the term “burning the midnight oil.”