Valheim Spawn Item List will let you create whatever item in the game you want using console commands. It's technically cheating, but Iron Gate Studio isn't going to stop you from using the console.
Valheim Spawn Item List: How to Open Console Commands and Enable Cheats
To start, hit F5 to launch the console. The command "imacheater" toggles the ability to use console commands. From here, you can enter the command "spawn [item name] [amount]" to summon whatever you want. You have to enable Cheat mode before you can spawn items.
Items are entered without spaces and with the first letter of each word capitalized.
A full list of items and their specific command codes can be found with this helpful Steam community guide by Sonata.
Cheats work as expected in single player, but only the host player can use them in co-op play. You may have to enable yourself as the Admin in your server files if you have trouble using cheats.
Cheats can be useful to jump ahead in the game if you want to explore possibilities, or if you find yourself completely stuck and the seed you got is particularly unforgiving. We'd recommend not using cheats on the first play-through, since that really defeats the purpose of a survival game.