What script should I use to save weapons when someone leave?

Hi there.

You'd want to look into DataStores. They can be used to save all sorts of data: bans, stats, money, you name it. Just be sure that if you use RemoteEvents that you protect them or exploiters can abuse them and break your game.

http://wiki.roblox.com/index.php?title=Data_store

Personally I would create a Folder within a Folder. Meaning a Folder than has a player's name as it and a Folder in that Folder that says "Weapons". In this "Weapons" Folder it has a bunch of values, possibly string values that has the name of said weapon so when you leave the DataStore can save those values in that Folder. Upon entering the game the Data can be loaded in and another script searches through the Folder to find the String Nameof the weapons in another possible Folder and load it into the Player's Backpack if you want that.

If that was confusing you could comment on my answer and I would be glad to clear anything up. If it did help don't forget to accept my answer.