Food-delivery startups from DoorDash to Uber Eats to Postmates are all now experimenting with different ways to maximize a restaurant’s kitchen — and in turn, generate more customers and more orders for partner restaurants. The delivery companies’ tactics range from deploying mini kitchen trailers to renting out extra space at fairgrounds to launching online-only companies. In a competitive market estimated to be worth $30 billion, each company is trying to play to its strengths to make sure it is the first app that a customer opens when they’re hungry.