Don't listen to her, she's Canadian!
I don't think placeholders should really be done, either, as we don't actually know how many items will be used. The design (and thus, implementation) of the menus will be greatly influenced by the selection of items, so focusing on creating an inventory system that will just be completely changed later on won't do too much good. As far as items are concerned, initial focus should be on creating functionality (which can have placeholders without fear of a complete redesign), simply mapped to buttons that won't end up being used as such in the game to test functionality of different item archetypes (such as thrown, swung, and conditional-use items) until the item selection and designs are finalized.
For example: In a basic engine test, we might map the 'I' key to test a thrown weapon prototype (such as a boomerang), 'O' to test a spell prototype, and 'P' to test a special item, such as an instrument system (Ocarina/harp/whatever).