ERC-1155.sol

// contracts/GameItems.sol
// SPDX-License-Identifier: MIT
pragma solidity ^0.6.0;

import "@openzeppelin/contracts/token/ERC1155/ERC1155.sol";

contract GameItems is ERC1155 {
    uint256 public constant COPPER = 0;
    uint256 public constant CRYSTAL = 1;
    uint256 public constant ELDER_SWORD = 2;
    uint256 public constant KNIFE = 3;
    uint256 public constant WAND = 4;

    constructor() public ERC1155("https://game.example/api/item/{id}.json") {
        _mint(msg.sender, COPPER, 10**18, "");
        _mint(msg.sender, CRYSTAL, 10**27, "");
        _mint(msg.sender, ELDER_SWORD, 1, "");
        _mint(msg.sender, KNIFE, 10**9, "");
        _mint(msg.sender, WAND, 10**9, "");
    }
}