Stuff is singular, things are plural

Hi Aurora! There is actually no difference between "I have stuff to do" and "I have things to do". It is more casual and informal to use 'stuff'. There is also no so singular form of 'stuff', whereas there can be just only 1 'thing'. I hope this helps!

Understand both. Say "things." You will hear both. They have the same meaning. "Stuff" is informal. "Stuff" is an uncountable noun. "Stuff" is also slightly disrespectful toward the things it is referring to. If you say "the room was full of stuff," I think of it as cluttered. I imagine a mixture of good things and junk. If someone said "The Museo del Palacio de Bellas Artes is full of stuff" it sounds strange, or like a joke, or disrespectful to the museum. If you say "I have things to do," they sound like important things you really need to do. If you say "I have stuff to do," it sounds as if you don't think they are important, and you don't really want to do them. "Thing" is an ordinary countable noun. If there is more than one thing, there are "things." "Things" fits every situation. It's not informal, and it's not too formal.

Ha ha ! their meanings are so close: one is formal, the other is slang. The two words imply the same thing. Your sentence structure however needs to be reviewed: I have things to do ( correct) I have stuff to do ( colloquial / slang) Hope this helps

I have things to do/ I have stuff to do (no “s”) Stuff is a collective noun, so there is no plural. There a lot of things/ There is a lot of stuff. Stuff is also more of a slang/ informal word