You can blow up rocks with rocket launchers or mine grenades.
You can get a wooden box and put it in a remote place. If it is built, you must destroy it. You can build it and shoot it out.
If the grid is not enough, you can find X: \ Factorio \ data \ base \ prototypes \ entity \ demo-entities.lua in the game directory. This document.
Then open Notepad, ctrl+F to find inventory_size, and then modify the following values to increase the number of backpacks. If you change it too high, you will not see it. We recommend 120, which is enough.