To jest potrzebne do lekcji. = It is useful for a lesson/for lessons.
also you can say:
To jest potrzebne na lekcję.
and also:
To będzie potrzebne na lekcji / w czasie lekcji /podczas lekcji = during lesson
dla lekcji
If by saying "something for the lesson" you mean: something which will be needed on one of the lessons i.e. tomorrow - it's "rzeczy potrzebne na lekcje/lekcję" things which are generally needed at school, the general term for pens, notebooks etc. - it's "przybory szkolne"
Dzisiaj mam coś nowego do lekcji. = which is thematically connected with the lesson, I associate it with sth new to talk about etc...
Dzisiaj mam coś nowego na lekcję. = sounds almost the same.... but I would say so if I prepared something else than the handout for my students ... something material. But it's my way of distinguishing the two. You can use both without taking care of the nuances!