etiquette for bundles/packs

Ask the GA creator (or check the comments for a similar question) and act accordingly. If you get no response, do what you feel like; if you enter and it turns out the creator isn't OK with what you already have, he will ask for a reroll.

The only one I don't have in that type of thing is when the Breath of Fire/Cthulu Saves The world comes up, because I already have Cthulu Saves the World, which I don't enter because it feels a bit scummy to take one and let one be completely useless.

Technically, it's against the rules as you are entering a giveaway for games you already own.
However, some gifters dont mind you joining.

I hide them with the steamgifts plus addon, so if I forget what I own I won't try for them accidentally. :)

Many times a giveaway creator will say things like "it's ok to enter if you already own 2 of these games" - but they are just being nice. You can ask for a reroll if a winner owns any of the package.

I never enter a giveaway (on purpose, at least) if I own any part of it unless the description says it is ok.