The container item can be anything with the custom model data
"385024961"

Press shift while holding the container in the off hand and the fireworks in the main hand

Use the fireworks in the container by flying with an elytra.

Event if this plugin doesn't implement commands, you can modify the amount of stored rockets per player using the /scoreboard command.

Are there any permissions?
No

What if I need to add something?
You can contact me on discord if you need somthing. For sure at 100 downloads I'm going to develop a new version following your suggestions.

What if I have a problem?
For any trouble join my support server.
https://discord.gg/QMf5ge5NDM

Is there a way to customize it?
Only by modifying the source code.

How can I access to the source code?
The only way to do that is to unpack the jar file.

Can I modify this plugin?
Of course, as long as you don't publish your version without linking this page.