when do I use 东西 instead of 件事 to express "something" From what I've seen 东西 is used when talking about food. Are there any other times where you use it instead of 件事？

Examples:

我想吃一点东西。

我告诉你一件事。
「東西」 means a "thing", a generic word for any object. 「那是甚麼東西？」 "What is that thing?" Food is obviously a subset of "things". There are many times you can refer to an object as 東西, like a toy, a pen... you name it.

「一件事」 is referring to an event (事件), or something that has happened.