A cubes most positive and negative x values

Hello, im creating a 3D snake game and I'm trying a new way to spawn the food on the game area. Until now I had borders and I instantiated the food in a random range between those 2 borders. I want to build a little bit more complicated levels now that have areas that are not just a square and i was wondering if i could set the area in which the food spawns in another way. What i tried is creating a cube which would be used as the floor and im trying to get a random x and z value on the cube. I thought maybe there was a way to get the most positive x and the most negative x of the cube and use those two for the random range. Is there a way to do this? Or do you have me a much simpler way to achieve what i want?