Hi Marc,
Those are spare track links - track links that are stored somewhere on the hull to replace broken track links.
The track sprues in your kit is the same for many, perhaps all, Academy M113-series releases. Some of those versions may have spare track links, others may not. Your references should give you a clue.
This M163 have on spare link in place, and below it you can see the mounting points for a second link:

Again: your references is your clue. If the vehicle you are modeling have them - add them.
Hope this helps.
Cheers,
/E