In the section “Categories”, create categories for your goods and categorize them accordingly. Then the section “Goods and Services” will be a much better help.
Set up “sizes” for your goods in the section “Properties” and add them in the goods card in the section “Goods and Services”. You can now carry every size separately. Try it: you will find it very easy to use!
Create a storage for your delivery person, and set him up as a user with access to the operation “Sale” at his storage. Then he will be able to make a “Sale” of goods directly at the customer's location, and you will know what your delivery person has sold and what remains for each order.
To make your accounting convenient, set up separate storages for each delivery person or delivery provider and move goods there for delivery. When the delivery person comes back, make a “sale” from his storage
Create a separate storage for each of your affiliates. Until goods are sold, they are yours, although stored at the affiliate's storage. When the goods sell, document this with the operation “Sale” from your Affiliate's storage to the customer “Affiliate”
Create the operation “Donation” in the section “Operations” and use it to make the donation. Remember to add access rules for the new operation in the section “Employees”