I was wondering if you could possibly duplicate items in Stardew Valley.
I want to try to make a really good farm layout, but obviously don't have all the resources for it.
There is, yes, though it may depend on what device you're playing the game on. The 'Stardew Valley Item ID Glitch' allows you to spawn items that you can then sell to generate resources you want. You can perform it by naming either your character or an animal you own after the game's item codes. By doing this, the item will spawn every time that name is referenced (so, whenever you talk to the animal). Also, you can find all game item codes at this website. So, for example:
In an interview with IGN, the Stardew Valley developer confirmed he finds this glitch charming and doesn't plan to patch it out, so it can be used without fear:
“I am aware of it, but I don’t think I want to fix it,” Barone said. “It's not game-breaking, it's kind of amusing, and the likelihood that someone would randomly stumble upon it is extremely low. So I feel like it's okay to leave it, and actually kind of fun.”
However, this is no longer possible on Switch as of December 2018 (version 1.3), as Nintendo mandated that that the glitch be fixed there.