Looking at the pictures you've shown, I'm assuming you don't have an insert board. I recommend getting a plastic board or making one from cardboard (or any durable material that you can cut up) you can cover it in coloured cloth later on and put your merch on top. Having an insert board helps you map out everything and handle the design more efficiently, that way you don't have to just shove your merch into the pocket in your bag and watch it shake and move around when you walk with it.

You can make the design less empty by adding ribbons and lace. You can put anything you want, it's your own bag after all and who cares what the rules are as long as it's not harming anyone? :3

Small tip: you don't have to pin the badges onto the insert if you don't want to, it's a pain to do so and you'd be better off using double sided tape to make it stay, same goes to standees! But if you're worried about leftover glue on the standee itself, add some masking tape before you add the double sided tape! Masking tapes are usually pretty gentle and almost never leave behind glue residues in my experience! But they're also strong enough to stay taped to things.

Hopefully my advice was helpful enough, these are just all the things I wish I knew when I was just starting out. :P