Use turbowarp: https://scratch.mit.edu/projects/612485186/

you can click around and stuff
I have everything else working, but how do you make items stack

This depends how much you want to stack the items to. If you're doing something like paper minecraft, and it stacks to 64, you can make 63 number costumes and a variable to control it. So when you get the first one, it shows it your inventory. But when you get a second one, the variable detects that and makes the sprite show, and switches its costume to 2. Once you get three, that's the variable and so the costume changes again. But then again, this depends how large your project is. If you need help with anything else, just hit me up at @zeldafan333 .
Cheers!
-zeldafan333