When you are on the product's details page, just click "Add to List" to display your previous purchase lists or to create a new one. You can get back to these lists at any time by clicking the big heart symbol at the top right of your screen or under My Account>Purchase Lists.
Collaborating as a team of buyers or need approval from the business owner? Your colleagues don't need their own account to view your purchase lists. Just go into the purchase list and copy the URL shown at the top of the list. Then send this to your colleagues in an email.