“Let's just not bother cooking tonight.”

Last night, you had a party and you have a lot of leftover food. You don't want to cook tonight. You suggest to your family:

Let's just not bother cooking tonight.

let's not (do something)

When you want to suggest that people in a group not do something, you can say "let's not ___". For example:

Let's not go out tonight.

You use "let's ___" when you're suggesting something that you're sure the listener will accept. In the example above, you think that everyone will agree that it's a good idea not to cook.

not bother (doing something)

The phrase "not bother ___ing" means to not do something that isn't needed. For example:

Don't bother washing those — I'll put them in the dish washer later.

I don't bother shaving on the weekend unless I have to go out to meet with someone.