When it comes to Jr High trends, its all regional I'm sure.
My dd13 has a Lands End backpack that she's used to 2 years and will continue to use. This gets her gear to-from school. They aren't allowed to wear backpacks to class... kids need to keep them in the locker.
For between classes she (and many other girls) use drawstring sacks to carry supplies. She's not picky about the big backpack... but was picky at the drawstring sack. Adidas, Nike, etc... they all run in the $20 range so I let her get whatever she wanted. Hers is an Adidas that is mainly black with some neon piping.
Other girls will carry canvas purses/backpacks. Frayed to look distressed.
Around here it's very important to "look like you don't care about appearance" even if you very much took a lot of effort to put your look together.
In my opinion it isn't the backpack that is going to matter... its the smaller bag/purse that they will carry in the halls.
As a caution, my friend/neighbor got her dd matching EVERYTHING in a pink Vera Bradley pattern before her daughter started 6th grade Jr High. Must have spent a small fortune. Matching backpack, lunch kit, lanyard, ID case, etc., It was mostly discarded soon after school started. My dd (a year older than her) confided that she looked like she was "trying too hard" that 1st day of school.