Using names of characters of cartoons, brands...

Good question...

By the sounds of it, you are referring to films, cartoons and so forth in a story, and this should be fine. If, however you had He-Man suddenly appear, and enlist your characters to fight Skelator, then it would have to become fan fiction, and thus non-commercial/profit.

In terms of companies, if you are smply referencing them, that should be fine. If you are saying they were plotting to go and wipe out half the planet, it would be wiser to come up with a fictional company, because you run the risk of being accused of damaging the reputation of said business.

Hopefully that helps a bit?