Thanks Claire. This would normally be handled via the sales team adding the POS item to the order (see How do I sell a stock item in Breww (e.g. glassware or t-shirts)?) and then the stock will be tracked for you.
Are you looking for a way for a dray to keep a supply of common items in the vehicle and drop them off with a delivery without them having been added to the order originally? If so, I’m sure this is something we could look at but it would need it’s own feature request as would be a much bigger task than something that could “just be added” at the same time, if that makes sense 
I can split this into another thread if that’s what you’re looking for and the method of adding them to the order won’t work as well for you?