
There is now an official response on if this works with backpack.
It does.
'To answer your question(s):
We are planning to address “Geared Up” in future errata, which should help in clearing up any confusion about the way it interacts with other cards. “Geared Up” will then say: “Permanent. Limit 1 per deck. Purchase at deck creation.
Forced - When your first turn of the game begins: One at a time, play any number of Item assets from your hand, reducing the cost of each by 1. During this turn, you have 3 fewer actions to take.”
In this sense, “Geared Up” will work similarly to “Ever Vigilant”, and each card put into play with “Geared Up” will resolve fully before the next one is played.'