Weird, they had this topic over at CoG not long ago. (Barely got any attention since it didn't involve the fascinating topic of the use of proper gender sounds or something)
If it's a humorous/casual story, you can use them all you want for the most part.
I think you can get away with it a little in certain places in a serious story like if it's the phone ringing or something else inanimate making a sound that the protagonist is reacting to (or will be reacting to)
I wouldn't use "Roar" for a lion though. I'd probably just say "The lion roars at you." Even with the cat and "meow" I probably wouldn't write a separate meow sound either. I'd probably be more inclined to use "meow" as dialogue for the cat that its crazy owner is talking to if anything.
The stuff like KABOOOOM! also gets a little too comic book like.
And yeah, I think italitcizing or bolding the words helps if you are insisting on doing it at all.