Custom Started Gear is an amazing mod that will let you decide what starter items players will have in their inventory when logging in into a world for the first time. This will be very useful when playing with your friends on your server. Here's a guide on how to use the mod :

Put all the items you wish players to start with in your inventory (Note the slot in which you place them will also be saved)
Then run the command "/csg_config set" to save your inventory.
Now when a player logs in for the first time they will get an exact copy of your inventory. (Including item NBT and meta, as well as armor equipped)

If you want to manually give a specific player an inventory, you can use this command : "/csg_config give <player>"

Download links are given below.

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Custom Started Gear Mod