There is a best way of doing that.
If you are using Odoo 17 then in settings enable "Purchase Agreements". Now new menu will appear in Order-> Blanket Orders. 
Create new Blanket order and in Type field select search more because by default in Odoo 17 only "Blanket Order " Type is created. In new pop up select new and you will be redirected to new form.
Write name as per you need "Purchase Template"

Update settings as shown in Picture.
After saving it go to Blanket form again and make sure this type is selected.
Now in product lines add your products you want. Make sure no vendor is selected if you want to use it globally for all vendors. Image is attached below for your reference.

You don't need to set anything else in it.

Now when you will create new RFQ then in Blanket Type field select this template then all products and their quantities as described in template will be added you can manually change them as per your need. If you selected vendor in Blanket Order form then this template will only be shown on RFQ in which that vendor is selected.

If you are using Odoo18, menu will be this: orders-> Purchase Agreements
Create new purchase agreement and in Type select "Purchase Template", because its already created in Odoo18 and configure other things as you want and usage is same as described above.

Hope you will find this solution well suitable because it's the standard way.