Trying to say 'other than' with nouns

I know I should already know the answer to this, but…

I am sure that I have tried every possible way to say this–I am trying to create a rule that does not allow a player to enter a certain entrance while holding more than one of two particular objects–and one of these objects is a holdall(a backpack), the other allowable object is something with a handle, but the player cannot carry both–in the usual way.

I am wondering why this clause will not work–(and this is under an “if the backpack is carried by the player”–the player will be able to ‘carry’ it, but not wear it.)

if the player is carrying something other than the backpack: say "You might want to stow, into your backpack, what you have in your hands, before you go into that passage."

This was supposed to disallow entry if the player is carrying one or more things in addition to the backpack.

I tried various other ways of saying it, in fact my first attempt was–

if there is something which is carried by the player other than the backpack

(This returned two error messages.)

Can someone please enlighten me??

Thanks.

Try

if the player is carrying something that is not the backpack

Thanks, Mike. It worked.