Okay so the bags you're going to put the inserts in ... are they consistently 12 cm wide? Are you measuring on the outside or on the inside? If on the inside ...
I'd do a little 'box' with those dividers. If you didn't need every last centimeter of the 30 centimeters for the fan and pamphlets, I'd make everything an inch smaller than your original measurements (so cut the fabric to the exact measurements you have and use a half inch seam allowance ... or quarter in if you want to have just a half inch of extra room). I think that'd let you get it in and out more easily. Since you do ... well, I don't know if there is a way. If the pamphlets are 30 cm and they just fit into the bag, then putting something else into the bag has to be smaller, or else it won't fit into it. Could you leave the ends off those parts?
Or - here's an idea - make a box for the smaller stuff (the pocket type things and the drink holder) and then have two flat inserts that are just basically walls that separate the fans from the box? I'd definitely use stiff interfacing so those walls can stand up on their own.
Not sure if I've made sense or if I've helped, sorry! Good luck!
I can't wait for partners! And I'm with you, pixieval, I want a real life Craftster friend too! (And seriously, it's taken me this long to figure out why I haven't been getting emails that this thread has been updated ... because I didn't actually posted in it. Whoops.)