Hi,
You can see guidance here:
Catering
If you take sandwiches, or other items of food and drink, to buildings in order to sell them, but have no contract or agreement to do so, this is not a supply in the course of catering and you can zero rate any item that is eligible, you can see guidance here:
Food products (VAT Notice 701/14)
However, if you are supplying the food or drink under a contract, for example to cater for an event, you are making a supply of catering and all your supplies will be standard-rated, unless the catering is supplied on-premises, in which case it will benefit from the temporary reduced rate.
If you make a charge for delivery you should read Postage, delivery and direct marketing:
Postage, delivery and direct marketing (VAT Notice 700/24)
Thank you.