Putting things in an 'I do not consent to the search of this bag' bag

And signing it.

Do you think this would just be an overall good idea? Would it even work?

I'm not sure what you mean, but all you need to do is never give consent to a search of anything. A writing will not help you, if anything they will use it against you in court. If they ask never say yes, because they will search your grandmother's car, house, purse, etc if she gives permission. Try to give your lawyer everything you can to work with.

From Experience..you tell a cop he cant search your car...Hell have your ass sitting on the side of the road till he has a drug dog come up