Thank you Kosta, this is the information I have been looking for.
I was at a toss up whether extras were a quick item slot so you spent less actions on retrieving an item (grenade, tools, etc. that you might need right away), or if it meant upgrading the suit itself in some way (all suits had some of the special suit features, but not all of them). What I find interesting is that without any explanation, different interpretations based off of the rules began to emerge.
To avoid confusion in the future, I would suggest adding Extras and its description to the Equipment Features list on the top of page 95. In that description, it would be useful to point not only to the Exo & Delving Suit Features on the bottom of the same page as accessories that could be purchased (if I read Kosta's explanation correctly), but also to the chart found on page 103, Weapons & Armor Accessories.