3. FB Jason Cabinda
Cabinda had a rough first two preseason games, which further put him on the wrong side of the roster bubble, before a bit of a rebound performance in the finale. He made the roster as a core special teamer and an overall team leader. He's also a leader and example for his teammates off the field, with the excellent work he does in the Detroit community.
Cabinda is only really a fullback by position label though. When the Lions use one (rarely) he'll see offensive action, but him touching ball it's not anywhere part of the plan. There's a reason he was on the roster bubble all offseason, even before such talk was a prominent topic once camp started. In a results-based business, the tangible on-field impact just isn't there here.
The Lions likely chose to keep Cabinda on the 53-man roster over a fourth tight end who would have a similar role. That fourth tight end surely would have been Darrell Daniels, who coincidentally or not was the final player added to the initial practice squad by the Lions.
Cabinda would almost surely be No. 52 or 53 on the aforementioned roster ranking. If he's not replaced by Daniels on the active roster, it will surely eventually be someone else before too long.