How did plants survive without the sun? If the creation account is describing physical events in the sequence they occur, the plants were created during the day on the third day and the sun during the day on the fourth day. The time the plants would need to survive is less than 24-hours:
And there was evening an morning the second day. (1:8)
Plants created during the third day (1:11-12)
And there was evening and morning the third day. (1:13)
The sun and other stars created (1:14-18)
And there was evening and morning the fourth day (1:19)
Plants are able to survive short periods of time without sunlight. Given how the events are described, it is possible the duration of time was comparable to a single "night." (If the events are taken as literal truth, that is, a day is a 24-hour day.)
A greater physical quandary would be how plants were able to germinate without the sun. That points to a sequence that requires a creative act of God. The sequence of plants and then the sun both defies nature and places the sun in a position of secondary importance to plants (including trees). Later men will see the sun as one of the essential elements of the natural world on which life depends. This will lead to the idolatry of worshiping the sun as a type of god. In that regard, the creation account in the Hebrew Bible sets itself apart from other ancient myths and reinforces the point that God is the true source and support of all life (from the moment the first plant was made).
The second aspect is on light created on the first day. Does the creation of the sun and all of the other stars on the fourth day relegate the light on the first day to a figurative action?
Both the Bible (taken as literal truth) and the natural world answer: no.
Light is an energy emission from any matter. Individual atoms can emit a single photon of light. A group of atoms, such as a star made up of hydrogen, emits light which is visible because the number atoms emitting photons is large enough to be seen.
The "big bang" is the current natural theory of the origination of the universe. This event started a sequence of events which would lead to the formation of hydrogen and helium atoms. It was also accompanied by enormous heat. That heat would cause any physical particle (that could) to emit light. An example from the world which we are all familiar is a fire or a hot stove where light is emitted from objects like wood or metal.
According to modern physics, 24-hours after the big bang the universe was a place of an incredibly high temperatures. So despite the absence of any stars, the universe would be place of an incredible amount of physical light. In fact, the amount of light after 24-hours would be greater than the amount at any point in the future. The reason is that on the first day, all matter would be giving off light, not just some as in the current state.
Not only is the light on the first day not figurative, it correctly describes what a modern physicist believes happened.