Grip editing won’t give you the best results if the tool is supposed to be anywhere but the player’s hand. You should be attaching models to players independent of the tool other than the equip events.
My personal favourite method for attaching items to players is to use accessories and the attachment setup already found in players. You can use the method below to find out how you can attach things to players (in your case though, instead of RightGripAttachment, you’d be using BodyBackAttachment):
I made a semi-related post to a thread which involves attaching items on the player’s back and switching them to the hand to be held. You can follow the first part of the post which involves attaching items to the player’s back:
Naturally with this method you’d have to change around some of your code if you want to modify the bag or anything - that meaning you’d be accessing the accessory to apply your changes instead of the tool. Not too big of a switcharoo though, still manageable.