Amber/Jerri is a big one where the tagalong went farther.

Heidi/Jenna, Cirie/Aras, Sean/Vecepia, Gregg/Jenn, etc. are some other examples. Some would probably disagree with those people being tagalongs, but I think editing-wise they got the shaft partly due to their more dominant and interesting friends
Heidi/Jenna and Cirie/Aras are completely ridiculous examples. If anything, Heidi (and Shawna) were Jenna's tagalongs. Jenna may have not been the most popular of the 3 girls, but it's not about popularity, it's about who's calling the shots, and that always appeared to be Jenna. And the Cirie/Aras thing is just baffling. Aras and Danielle were running things on their tribe from the beginning, and Cirie started off at the bottom of the totem pole and slowly worked her way up to a position of power. None of those people were tagalongs, the tagalongs were Shane and Courtney.

Anyway, some examples of tagalongs who made it further than the people they latched on to:

Amber outlasted Jerri.
Amber outlasted Rob M.
Erik outlasted Jaime.
Gina outlasted Hunter.
Jan outlasted Helen.
Jason outlasted Mikey B.
Jenn outlasted Gregg.
Katie outlasted Ian.
Kim M. outlasted Jeff W.
Matt outlasted Rob C.
Vecepia outlasted Sean R.

And now it looks like Alexis will outlast Joel, and Natalie may outlast Alexis.