As people have said above, masks are optional on domestic flights.
My husband flew two months ago, two separate round trip flights. On Southwest less than ten passengers had masks on and the flight attendant on both flights said during the pre-flight announcement that they were happy to see everyone’s faces. On American Airlines all flight attendants had masks on and about 70% of the passengers, and during the pre-flight announcement the flight attendant said to please respect passengers who choose to wear a mask. All flights were fairly large Jets, 727 and 737’s.
You can bring food through security as long as it’s not a lot liquid. You will have to buy beverages on the gate side. You can buy a meal or snack to go gate side also. Meal service on the plane varies by carrier, you might want to call the airline you choose to see if there is meal service. All flights will likely give you a snack and beverages, but the snack might be a very small bag of pretzels or cookies.
Tip: it might be more relaxing to get to the airport early, eat a meal at the airport, and bring some sort of small snack on board. Then you don’t worry about traffic getting to the airport or how much time it takes to get through security. If you run late you can always buy food to-go at the airport to take on the flight.