Candles Need a licence, which can be arranged with the venue by the producer. Tend to be difficult for actors to light or inclined to blow out. Electric ones, especially with flicker bulbs can be quite an effective substitute, but check the batteries. Lots of plays involve the symbolic destruction of something on stage every night. This may be a sheet of paper that gets crumpled up or torn, a piece of crockery that gets dropped and broken or a length of wood that is smashed over someone's head.
Balsa wood is good for making breakable things.
There is often a need for bottles or glasses to be used on stage. There are two popular solutions. Alternatively, plastic glasses could be used. The props store has a limited range of them, and they can be bought from shops such as Robert Sayle. Buying convincing plastic glasses is certainly more expensive than going for a box of factory-rejected real glasses, though.