Learn Dutch: We nemen dit voor de zekerheid mee. - We are taking this with us just to be sure.

While voor het geval dat means "in case" and introduces a specific subordinate clause (like "in case it rains"), voor de zekerheid is a set phrase meaning "just to be sure" or "as a precaution". You use it when you don't need to specify exactly what might happen.

What is the literal translation of voor de zekerheid?

It literally translates to "for the certainty". In natural English, we usually say "just to be sure" or sometimes "just in case" (when used on its own without adding "that it rains", etc.).

Why is the word mee sitting all the way at the end of the sentence?

The verb here is meenemen (to take along / to bring with), which is a separable verb. Because this is a regular main clause, the conjugated part (nemen) takes the second position, and the separable prefix (mee) gets pushed to the very end.

Why does the object dit come before voor de zekerheid? Could I swap them?

You shouldn't swap them. In Dutch word order, specific direct objects (like the pronoun dit, meaning "this") generally come before prepositional phrases like voor de zekerheid. If you were talking about a non-specific object, like taking "water" with you, it would typically come after: We nemen voor de zekerheid water mee.