The inventory box should automatically resize itself as you pick more items up, until it reaches the "Maximum slots" value in the InventoryBox element's properties in the Menu Manager.
To make the inventory pop up in various ways, first create an ActionList that does the actual menu handling: make a new ActionList, and give it a Menu: Change state Action that turns on the Inventory menu. If your Inventory menu's Appear type is set to During Gameplay, you'll have to lock/unlock it - otherwise if it's Manual then turn on/off will be what you want.
You can then call this ActionList when another Menu Button is clicked on. Again in the Menu Manager, you can set a Button's Click type to Run Action List, and then be made to run your new ActionList when clicked. You can find a variety of tutorials on menus here.
You can also call this ActionList when an input listed in Unity's Input Manager is pressed. Define a new Input axis called OpenInventory, and set it's positive/alt buttons to your input key and mouse button 2. Then you can use AC's Active Inputs Editor to trigger the ActionList when this input is clicked - you can read more about Active Inputs in section 2.14 of the manual. Active Inputs and new button clicks are also covered in the 2.5D tutorial, starting 1:46.
Comments
To make the inventory pop up in various ways, first create an ActionList that does the actual menu handling: make a new ActionList, and give it a Menu: Change state Action that turns on the Inventory menu. If your Inventory menu's Appear type is set to During Gameplay, you'll have to lock/unlock it - otherwise if it's Manual then turn on/off will be what you want.
You can then call this ActionList when another Menu Button is clicked on. Again in the Menu Manager, you can set a Button's Click type to Run Action List, and then be made to run your new ActionList when clicked. You can find a variety of tutorials on menus here.
You can also call this ActionList when an input listed in Unity's Input Manager is pressed. Define a new Input axis called OpenInventory, and set it's positive/alt buttons to your input key and mouse button 2. Then you can use AC's Active Inputs Editor to trigger the ActionList when this input is clicked - you can read more about Active Inputs in section 2.14 of the manual. Active Inputs and new button clicks are also covered in the 2.5D tutorial, starting 1:46.