I didn't do much.= I just did normal things like housework, watch TV etc I just had something to eat= I ate a simple meal, for example a sandwich I had an early night = I went to bed before midnight or earlier.

I think he's answering a question: "What did you do last night?" And that is his answer: "nothing much" = hardly anything He had something to eat, and had an early night (=went to bed early), so yeah, he didn't do much.

The person had an uneventful night. Likely he/she went home early, ate something, then went to bed. He/she is telling someone that they did not go out that night.