「(Phrase) + の」 always modifies a noun that follows. That noun can either directly follow 「の」 or after another phrase that directly follows 「の」.
To examine this in your examples:
「そのようなリスクを少しでも減らすための」 modifies 「チェックリスト」.
「普段はIT企業の役員を務める彼の」 modifies 「バイト代」.
「『未来篇』のBD-DVDの」 modifies 「販売」.
Unlike in many other languages including English, the use of commas in Japanese is pretty much left to the discretion of the writer and that often seems to be the cause of confusion and misunderstanding among Japanese-learners.
In your examples, the comma would feel least "needed" in #1 because the noun 「チェックリスト」 follows directly the の-phrase. The author probably used a comma because the の-phrase is fairly long and s/he saw a need for a "moment of pause" there.
The commas in #2 and #3 seem more "needed" (though still optional) because in each case, there is another shorter の-phrase between the main の-phrase and the noun that it modifies.
Finally, the possesive の that you mentioned at the end has very little to do with the 「の」 that I have discussed above.