A. In principle if there are articles that are considered Muktza inside the knapsack at the beginning of Shabbos even during sunset, the knapsack would be considered as a 'Bosis' or base and foundation supporting the Muktza and thus become also similarly Muktza as ruled in Shulchan Aruch (O.H. 309).

One issue would be what kind of Muktza. If money was placed inside the knapsack, since money is not a usable utensil per se, the type of Muktza would be more stringent, and cannot be moved at all.

Horav Shlomo miller's Shlit'a opinion is that credit cards or similar may be considered a utensil, since they could be used to open a locked door.

Obviously, a cell phone is a utensil, but similarly to the cards it is Muktza as a Keli Shemelachto Leissur, or prohibited to touch and handle because it is used for forbidden purposes on Shabbos.

However, this type of Muktza is more lenient than a non-utensil Muktza, and it is permitted to touch and move when one requires the use of its space or even the item itself, as when used for a permitted purpose. An example would be using a carpentry hammer for cracking edible nuts.

Horav Shlomo Miller's Shlit'a opinion is also that the best way to handle your case if you need to use or move the knapsack during Shabbos. is to place before it begins the Muktza articles at the bottom of the knapsack, while the permitted articles you need should be placed on top.